I came across a fallacy classification that I had never heard of today: The Fallacy of Limited Depth. The fallacy is when an argument or theory fails to identify an underlying cause, and instead appeals to membership in a certain category.
When talking to woomeisters, specifically those who subscribe to one of the various "toxin" ideas, I have struggled to articulate why it is not good enough to simply say that "substance A contains theoretically dangerous substance B, therefore substance A is bad." My usual response is that "the dose makes the poison," but this is unsatisfying to many -- particular when we are talking about anti-vaxers, because of course the usual response is that babies' metabolisms are different and therefore it is difficult to say what dosage could be damaging or cause developmental issues.
I think "the dose makes the poison" is a partial answer, but the other part of the answer is that they have committed the fallacy of limited depth. To assert, for example, that there is formaldehyde in vaccines, and then move on as if this was an argument in itself, is to commit this fallacy, because no mechanism has been provided by which such a small amount of formaldehyde could be harmful. It is simply a categorical association, i.e. formaldehyde is a chemical, it's used in embalming, therefore things that contain formaldehyde are bad.
Or another would be the "too many, too soon" hypothesis. There is a shallow appeal to the idea that a large number of vaccines in a short period of time could somehow be harmful, but without a mechanism, the hypothesis is fallacious. It simply appeals to the categorical similarity with other things where it may be possible to have "too much, too soon," e.g. like solid foods.
So I'll have to remember this one....