You present it as a dichotomy when that's not actually the case. I'm heterosexual and white, but I don't see how policies that e.g. allow gay people to marry - a stereotypically "liberal" position - harm me in any way.

There are some things where it's a zero-sum game, such as affirmative action. And those do in fact tend to be less popular even among liberals (as evidenced by referendums on those topics in blue states). But that's a relatively small part of the overall liberal platform.