How do you buy pasta now?
I do packaged food/beverages professionally, so I know what almost every ingredient I read on the label is there for and what it does, but I don't know the health ramifications of all of them (nobody does), how they're produced, etc. And I could not expect 99% of people to know 10% of what I do. They'd never have time to.
I also don't think we know exactly how it's getting into people. The EPA says the most common source is drinking water, and it's probably getting there through pollution, waste, etc. I'm not even sure they know that really though. That's the thing about large, complex de-centralized systems, especially ones that intereact with environmental factors: there's nobody who knows how the whole thing works.
And even if it's getting into water entirely through people cleaning their non-stick pans, which I'm sure isn't the case, I can't rely on everyone else in my water supply area (literally hundreds of thousands of people) to curtail their use. Probably tens of thousands of people in my area put a Teflon pan in the dishwasher today. I can, however, rely on the water plant to filter it if they're made to do so and there's testing done.
And, also, I'm very much of the "this hysteria is overblown" mindset. When you look into actual evidence of harms caused by the levels of PFAs most people are exposed to, all you find are very weak correlations. Outside of people exposed to very high levels of the stuff, there's no solid evidence of any harm at all. You can't do any sort of controlled test since it's so pervasive and also geographical in nature due to the drinking water issue. (Everyone in a target area is either exposed to it or not exposed, so to compare people who are exposed to those who aren't, you have to compare people in different regions, thus making your study not controlled as any observable effects could be due to some other regional factors.)
That said, absence of proof is not proof of absence, and I feel fairly sure they aren't good for us or 3M would be marketing them as a pharmaceutical. I think there's some chance they're bad, and they can be affordably filtered out with the money manufacturers are going to have to pay in settlements. I'm far from a big government kinda guy (quite the opposite usually) but tragedies of the commons, which this totally is, are very much the thing we need government for.
I don't see it as a process of people having to know everything so they can opt out. As you said, that will never happen in such a complex society. Instead, people can focus much more on opting in when they do reasonably know they trust a product. That can't always be done for sure, but touching the door handle at a store is much less likely to have serious consequences than the food I eat every day.
I may not have much say in what is already in my water but I absolutely have a say in what I spend my money on.
Firefighting foam is a great example of when a government intervention could be needed though. I don't directly interact with that product at all, I don't buy or use it. If its getting into my water then its effectively infringing on my rights. If a majority of people are willing to ban those chemicals knowing that it will make fighting fires more difficult, or impossible in some cases, then a ban makes sense as consumers are powerless there.