A couple problems. V's gender ambiguity is not a matter of opinion either. It is pretty explicit within the comic that characters cannot tell what sex V is (or their former spouse, for that matter). Its understandable that somebody would decide one way or the other (and many people have), but youre going to run into problems when you base a premise off of that decision, which the OP did.
Secondly, Miko's open mindedness about these matters is not a matter of opinion either. On multiple occasions she has been shown to be perfectly OK with the idea of sex and same-sex relationships.
So yes, in this particular instance, Kish is perfectly within his right to make an absolute statement such as this because he is, in fact, factually correct.