One of the hard parts about holding strong opinions is dodging dogma. You have to admit that there is room in any value-based viewpoint for reasonable disagreement. That doesn't mean anything goes, and it certainly doesn't mean that every opinion is equally justifiable. But there can be people who believe in broadly the same things but come to different conclusions.
For example, I think that a democratic socialist economy is the best way to secure my values of liberty, equality, and solidarity and to give everyone the best chance at a good life. More moderate social democrats and liberals have the same values, but they disagree on what those values need to look like in practice. It is a reasonable disagreement. We're on the same team, even if I think some things they advocate are misguided or even harmful.
Conservatives and libertarians, however, either have different values entirely or mean different things when they use the same words. From the point of view of a socialist, conservatives and libertarians are unreasonable. Their goals are different, their beliefs are different. I don't feel compelled to compromise with them; I want them to change their minds!
Of course this only applies in situations where the outcome of these issues affects all involved. Sports fans are as alien to my way of thinking as conservatives are, but their enjoyment of watching other people running around for hours doesn't affect me, so who am I to complain?