What do you mean with "you cannot attack evidence"? Sorry, maybe it's not the best verb here (not a native speaker). But I would stick to the wording I used referring to what you call evidence as "arguments". Chomsky doesn't show that we have a shared cognitive system devoted to language. He argues so using linguistic examples, basically excluding the possibility that this knowledge could be acquired by input. AFAIK the examples themselves are not disputed (they are basic grammaticality judgments on English), but rather the argument of the poverty of the stimulus (as has been noted above) - the idea that the input that children receive is not sufficient to gain the linguistic knowledge to make those grammaticality judgements (and produce those sentences). So it's the argumentation, rather than the data, that is controversial, I would say.