> What's wrong with just red team or blue team?

Because people care about different things and don't always align neatly with party policies.

Suppose I care deeply about both gun rights and abortion rights. Who do I vote for? Pluralistic systems with proportional representation are better at reflecting the values of the electorate.

> As long as they're both competing for your vote and not colluding...

Now say I want to tax the rich. That's got strong bipartisan opposition. Who do I vote for?