Most people, even you strict "individualists" would be outraged and horrified to find out a company suddenly decided to put ammonia in the food they sell and 100's of people died right away.
Those of us in favor of banning this stuff are outraged now...we don't need to see people die immediately to be horrified by the evil of knowingly putting deadly or illness causing chemicals in food.
I think you're conflating two distinct issues here:
- Should specific substances be explicitly banned by the government? The answer is no.
- Should companies be held liable for products that unexpectedly kill consumers? The answer is yes.
To demonstrate why these are completely separate issues, let's get away from aspartame and cyanide for a minute. Instead, what happens if a company has unsanitary practices and sells chicken breasts with extremely high salmonella content, and tons of kids die? Obviously, the company didn't intentionally put anything harmful or even questionable in the food, but it could be their fault anyway (let's ignore the fact that it was probably not fully cooked when eaten - for the sake of this example, let's say a bunch of salmonella survived anyway

). Obviously, it'd be ridiculous to ban either chicken breasts or salmonella. However, if the company had unsanitary practices, they ARE liable for the deaths. It's not murder, but whoever was responsible could be potentially guilty of manslaughter. You might say, "But we can make laws about salmonella content, too!" In that case, what if the company puts some kind of new additive in their food that the government doesn't even know about yet, meaning there couldn't possibly be a law banning it? Scores of people die. The substance isn't banned, but the company is STILL liable for the deaths.
Understand here? You don't need to explicitly ban harmful substances from food to make the manufacturer/processor/etc. liable. If a company intentionally put ammonia into a food, everyone responsible would be FUCKED (at least in a free market, where there's no corporate veil). FDA or not, if a company ever put anything into a product that caused immediate death, there would be some serious repercussions. Actually, to cement the idea that liability is separate from banning specific substances, let's change course for a moment and consider a gun manufacturer. The government doesn't HAVE to say, "It's illegal to make your guns explode when the trigger is pulled." Despite that, if Smith & Wesson made a gun that is engineered to explode and blow off your arm when you pull the trigger,
you'd better believe they'd be considered liable. After all, they marketed it as a gun, not a hand grenade! That's some serious fraud when it leads to an injury like that. The same goes for poisons marketed as food.
Now, obviously, aspartame doesn't cause instant death - rather, it causes chronic health problems that are not immediately noticeable. However, that's actually a good reason not to ban it outright. Let's say, just for the sake of argument - what if we were wrong about aspartame? Obviously we're not, but my point is, what if the government decided to ban some kind of additive that is not unsafe? As a matter of fact, it does this ALL of the time, because the FDA is in collusion with the big fish. You have to remember that whenever you give the power to regulate something, that power immediately becomes the property of the highest bidder, e.g. Monsanto. If we ever allow the government to ban specific substances, it will BAN the wrong ones and ALLOW the wrong ones...and what happens then? With the blessing of the FDA, an unaccountable government agency, Monsanto is TOTALLY LET OF THE HOOK for the dangers of aspartame! It's no longer strictly their legal responsibility, because they have the explicit blessing of the government!
That, howmanysheepcanyouherd, is exactly why the federal government should not be permitted to ban or explicitly approve substances. No matter how well-intentioned you might be in saying we should do that, the end result will always be the same thing we have today. The only alternative solution is to trust the market to take care of it instead.
Now, who is liable for harmful products? Generally, the manufacturer is liable, but let's say private certification agencies pop up. Maybe as part of the certification process (giving their okay to some manufacturer's product and putting their seal on it), they agree to take on the liability for anything harmful in the product. After all, they're certifying it (and they might require ingredients, etc. to be put on the label as part of this process). In that case, it would be in their best interests to allow everything safe (more money!), but it would also be in their best interests to refuse to certify anything questionable or dangerous, e.g. aspartame. Contrast this with the FDA: When the FDA certifies something as okay, pretty much all liability disappears into a black hole. The company says, "The FDA certified it! It's safe - and if it isn't, blame them!" The FDA says, "ROFLMAYONNAISE, what are you going to do? Put us out of business?"
The market would be relatively quick to figure out which agencies were reliable and which ones were worthless or a bunch of frauds making backdoor deals. People would care to look for the seal of approval of their most trusted agency - otherwise, they'd refuse to buy products. This is a lot like how kosher certification works, except kosher certification is something like 95% of consumers couldn't give two shits about. Notice, however, that despite how few people care about kosher certification, most big companies are prepared to pay for inspections by these agencies! Imagine how widespread health/safety certification would become! Because of the high demand for safe products and the fact that liability doesn't disappear into the black hole of the FDA, this market model would eventually result in only safe products appearing on the market.
In addition, without the government able to make ridiculous laws on behalf of market leaders, products would be able to explicitly advertise themselves as, "Free of the dangerous BLAH BLAH additive put into SPECIFIC COMPETITOR NAME's product!" As long as their claims were true (i.e. not constituting fraud), it's totally legit to compete that way.
This is a totally separate issue, but furthermore, without monopolized media, consumers would be getting much, much better information about dangerous substances in their foods in the first place.
Finally, you're completely forgetting that the individual states are free to ban whatever substances they want - although it might be a bad idea.