Almost all of us have looked in horror at a packaged food with, literally, forty or fifty ingredients. The thought crosses all of our minds, "Do they really know all these ingredients are safe for me and my family?" Let me answer that for you: "No!"
In fact, not only do that know whether it is safe for you, but they do not care. Actually, I am sure that there are those in the food industry with a conscience, but my opinion is that those type of companies and individuals are few and far between.
Let me give just one example. In 2008 a journal article highlighted the dangers of a chemical called diacetyl, a chemical used to give buttered popcorn its flavor and added to many other products as well. Diacetyl has, after years of use, been linked to "severe lung disease" and a condition called "bronchiolitis obliterans". And guess what? Researchers found toxic levels, which is only a few parts per million, all over various facilites that they examined.  Now why would they put a chemical like this within ten miles of a plant that handles food?? Ignorance? I doubt it in this case.
In some cases, it undoubtedly is ignorance. Researchers recently found two food additives that are xenoestrogens, i.e. environmental estrogens that can impact us. The first food additive, propyl gallate, is a common preservative used to prevent fat spoliage in items such as baked goods, shortening, dried meats, candy, fresh pork sausage, mayonnaise and dried milk. The second additive, 4-hexyl resorcinol, is used to prevent discoloring in shrimp, lobsters and shellfish.
So, in the case of these food additiives, the food industry probably just never bothered to test whether or not these were endocrine disruptors. In my opinion, it is inexusable to throw a bunch of chemicals into something that people are going to eat just to add texture or a certain flavor or for any reason when it is has not been tested for years. (By the way, an increasing number of tainted products from China have been spread throughout the globe as well.)
This is what you MUST realize: the flavor industry is very mature and extremely sophisticated in knowing how to sell food. They know the exact chemical that gives marshmellow its flavor. They have equipment to analyze the hundreds of chemicals that make up the flavor of coffee or a strawberry. They know how to give something proper texture, color and crunchiness.
But, for all their culinary and chemical genius, they are creating a toxic cesspool in your kitchen. Common sense tells you that you cannot just take everything you come up with a chem lab and throw into your pasta sauce and have it be safe. But these people have no common sense and no conscience.
Here is another example: titanium dioxide. Titanium dioxide has been classified as a potenially mutagenic by the Internation Agency for Research on Cancer (IARC) as an IARC Group 2B, which means a "possible carcinogen to humans". Now one would think that something that is potentially carcinogenic would not be in any products, much less something you would put in your mouth, right? Wrong! It is nearly ubiquitous, being found in a wide variety of home and consumer products including tooth pastes and foods. The argument is that it is safe when consumed because it cannot get to the lungs, but I would argue, "Why put a toxic chemical into our food, even if it is toxic in a different usage??" Get the crap out of my plate and my toothpaste!
Another example is sodium nitrite which is added to meats and packaged foods containing meats by the bucket. Nitrites can in a heated environment (like in a frying pan), or, in an acidic environment (like in your stomach), create carcinogens. Now why would you pour that all over our meat supply? Of course, if you eat a plaque-reducing Low Fat Diet, you won't have to worry about that, but it still highlights the irresponsibility of the food industry.
By the way, this is only for the chemicals that you know about. If the packaging says "natural flavoring", "artificial flavoring" or "spices", you have absolutely no idea what they are putting into it. "Flavors" are considered proprietary and necessary to protect the manufacturer. However, what the consumer does not realize is that literally dozens of untested, unproven chemicals are thrown into the "flavor" mix and none of it is revealed on the package.
Look at what the ingredients that are hidden in a typical strawberry milk shake for example: "amyl acetate, amyl butyrate, amyl valerate, anethol, anisyl formate, benzyl acetate, benzyl isobutyrate, butyric acid, cinnamyl isobutyrate, cinnamyl valerate, cognac essential oil, diacetyl, dipropyl ketone, ethyl acetate, ethyl amyl ketone, ethyl butyrate, ethyl cinnamate, ethyl heptanoate, ethyl heptylate, ethyl lactate, ethyl methylphenylglycidate, ethyl nitrate, ethyl propionate, ethyl valerate, heliotropin, hydroxyphenyl-2-butanone (10 percent solution in alcohol), a-ionone, isobutyl anthranilate, isobutyl butyrate, lemon essential oil, maltol, 4-methylacetophenone, methyl anthranilate, methyl benzoate, methyl cinnamate, methyl heptine carbonate, methyl naphthyl ketone, methyl salicylate, mint essential oil, neroli essential oil, nerolin, neryl isobutyrate, orris butter, phenethyl alcohol, rose, rum ether, g-undecalactone, vanillin, and solvent ". 
This is all done by people called flavorists. Flavorists work their way through the food industry via an apprentice system. Some have Ph.D.'s and some have little education, but it doesn't really matter because it is considered more art than science. Our reaction to food has been scrutinized and microanalyzed to where they know just what chemicals to add to give it the color, crunchiness, gumminess, slipperiness and so on. In the industry, they call this the rheological (or flow-related) properites of food. Books have been written about the rheology of food and it basically boils down to throwing a bunch of chemicals into your food, many of which can be disguissed as natural or artifical flavors.
Another of my favorites is diethylene glycol, which is a nasty chemical that has caused caused deaths around the globe in various tainted and contaminated products. It is used in hydraulic and brake fluids, coolants and other industrial uses. It also makes its way into our food supply in trace amounts through polyethylene glycol, which is used in toothpastes, eye drops, and some foods. In the U.S. "only" 0.2% diethylene glycol is allowed in any ingested polyethylene glycol products.  Natural News reports that "Aldehyde C-17, flavoring for cherry ice cream, is an inflammable liquid used in dyes, plastics, and rubber. Piperonal, used in place of vanilla, is a lice killer. Ethyl Acetate, a pineapple flavor, can also clean leather and textiles."  Bon appetit!
You also often get a nasty dose of some very toxic chemicals in the packaging process of many foods. A great example is microwave popcorn which has a nasty carcinogen (PFOA) that vaporizes and disperses onto your popcorn when you heat it in the microwave. Somebody really thought that one out, eh? (Read this Wikipedia link for an extensive list of studies showing just how toxic this stuff is.)
Canned tomato products are other great examples in this category. Tomatoes are acidic and pull a toxin, bisphenol-A (BPA), out of the lining of the tin can it is stored in. BPA is a xenoestrogen associated with various reproductive disorders in animals. Even a very minute amount can have a negative effect. And in a recent Consumer Union study of various canned goods, the BPA problem was found to be much more widespread than previously imagined.  Almost every canned product tested, including green beans, Juicy Juice, soup, corn, chili and baby formula, had signficant BPA levels and researchers estimate that it would be very easy for someone to consume levels of BPA close and equivalent to that which caused reproductive issues in animals. I recommend that you avoid canned goods until the FDA sorts this out.
Notice that I have not even talked yet about Excitotoxins or partially hydrogenated oils. The bottom line is, unless you know every ingredient on the package and it does not say "artifical flavors", "natural flavors", "spices" or anything similar, don't buy it and don't use it. In general, it is much better to prepare your own food, even if it is simple, than to eat food prepared by flavorists and the food industry.
NEWS FLASH: Processed foods have just been linked to depression.  This is not surprising since they are full of excitotoxins, transfats, high glycemic foods and who-knows-what-chemicals and low in vitamins, antioxidants and minerals. Your brain, more than any other organ in the body, needs an abundant supply of vitamins and minerals as well as protection from free radical damage and poor blood flow. You will only get the opposite effect from processed foods.
1) J of Occupational and Environ Hygiene, Nov 2008, 5(11):679-688(10), "Diacetyl Exposures in the Flavor Manufacturing Industry"
4) The Brit J of Psychiatry, 2009, 195: 408-413, "Dietary pattern and depressive symptoms in middle age"