Paraphrasing from a real conversation:
A: Peanut butter causes cancer. So you should avoid it.
B: Pollution also causes cancer. Lots of things cause cancer. We can't avoid them, so there's no point in avoiding peanut butter.
I was left so gobsmacked I couldn't think of a reply, much less any kind of counterargument. I'm sure there must be something wrong with this argument, but I can't put my finger on what - it just seems obviously wrong but I can't explain why.
Is this some sort of fallacy? Can anyone tell me what it is? It's similar to the perfectionist fallacy, but somehow feels different to me.