There is always a point in having a discussion with someone, even when they are severely misinformed and blind to their own biases because neither of those makes their perspective void, just harder to understand. But gaining that understanding is the only road available to you that can lead to them changing their perspective. Additionally, no matter how much sense you make to yourself and how much nonsense the other individual appears to be spouting, the moment you dismiss even the possibility that you yourself are wrong and that they could have a valid point, albeit poorly articulated, is the moment you throw away the claimed high ground of being rational.