The form matters just as much as the quantity.

Similar with a lot of heavy metals.

For example seafood has relatively high levels of arsenobetaine, an arsenic compound. But it is rapidly excreted from the body. It is why you are supposed to refrain from eating seafood before an arsenic test.

Also, re: vaccines, we no longer use thimerosal (an antimicrobial) in most vaccines due to the public outcry, so it is irrelevant anyways. But yes it was a non-issue. Not to mention, children are exposed to significantly more mercury compounds from their diet and breast milk than was ever in vaccines.

Anti-vaxxers most likely not. But there are a decent amount of people on the fence. I'm not likely to convince them but maybe people close to them can.

In any case, we should all be cognizant of how these baseless panics can actually affect government policy if they get large and loud enough.