It’s fine to have dating preferences. The issue is when people who are just calling anyone who is conservative leaning terrible. If you don’t agree with someone’s political ideology, you should just respectfully disagree, not call them a terrible person.
Also, calling people evil for their options is a terribly way to convince them to change, it just makes them get really defensive. If you want to convince someone to change opinion, you need to have a respectful, insightful discussion.