Fair enough if you disagree with his stance, but none of that makes sense. For starters, holding a belief or ideology doesn't mean you support every outcome of holding those beliefs or ideals - in much the same way that supporting free speech doesn't mean you support hate speech.
As for Waters' views and how 'leftist' they are or aren't, his message and motivations currently seem the same as they have been for decades, and I'd suggest that a lot of those more greatly reflect left leaning views than right. There are of course instances where taking a more pacifistic approach to aggression is at odds with the notion of protecting the downtrodden - that's inevitable, in Waters' case it seems to me that leaning towards a more neutral position (which as Scaff points out above, unfortunately favours the aggressor in this instance) is the result of Waters disdain for Western military arrogance and foreign policy, and potentially also in part because in the back of Waters' mind (or the forefront of it - depending on which album you're listening to), is that the father he never knew died after abandoning his stance as a pacifist.
Whether you think he's right or wrong in his stance likely reflects where you stand on 'better dead than red' or 'better red than dead'. In crude terms, I'd say Waters very literally favours the latter, and that would firmly put him on the left in my opinion.
Also... "incel"... ? This is just getting on for "Everyone I don't like is Hitler" meme level debate.