Calling a particular site illegal might be libelous (if untrue), and while SO can probably deflect liability with the CDA, the answerer can't. So, the "no" answer is risky, legally.
Calling a particular site legal might get the answerer held liable if the questioner gets in trouble when it turns out otherwise. So, that's risky too (though, probably avoidable with appropriate disclaimers).
Lastly, "is X legal" is not really a computer question, even when it involves web sites, and none of the SO sites have an audience educated (e.g., law school) to answer legal questions.
I strongly suggest closing legal questions pertaining to specific, identifiable entities.
I am not a lawyer, this is not legal advice.