I never could understand the argument about republic vs democracy. Some people say republic protects rights of minorities because representatives are voting on

I never could understand the argument about republic vs democracy. Some people say republic protects rights of minorities because representatives are voting on laws, and there is a constitution. But if majority wants a law that is unfair to a minority, amending the constitution and electing representatives who dislike the minority is not much harder than voting for a law democratically. The only way this kind of argument works, is if representatives keep lying to get elected and then not keeping their promises. And from history we know this kind of lie never ends well. There can be systems where different people have different amount of votes, but the system of determining this should be known, and accepted by the people, to not cause instability.