If Conservatives are disappointed their leader didn't get elected, they should have supported electoral reform without playing political games

I'm not sure what the answer is to make them good-faith actors

Stick firmly to the facts. Don't get into emotional arguments, because it's a losing game. When discussing electoral reform, use hard data about vote percentages versus seat counts. Show how the system mathematically distorts representation for all parties including conservatives themselves. Present international examples where proportional systems work effectively. Keep bringing the conversation back to universal democratic principles rather than partisan advantage. When they make emotional arguments, respond with evidence, not matching rhetoric.

What's the non-extreme method of getting conservatives to stop hurting themselves and everyone around them?

Push for systems that punish bad behaviour. Proportional representation naturally discourages obstructionism because parties can't gain majority power with minority support. It creates structural incentives for cooperation and compromise rather than trying to change individuals' character or beliefs. Under PR, parties that refuse to work constructively become irrelevant because coalition-building becomes necessary. The system itself becomes the accountability mechanism, not partisan battles or public shaming. Electoral reform is the non-extreme solution because it works with human nature rather than against it.