I'm not talking about becoming centrists, i'm talking about building coalitions. There are core issues many people can agree upon, and treat each other under the motto "the enemy of my enemy is my friend". Details can be discussed later, when the threat is less urgent. History has a few examples on what happens, when the left treats other democrats as the enemy. The most infamous one should be the German KPD. They declared the SPD and social democracy as the main enemy. I don't think i need to point out how that ended. The thing about democracy is, that you will never get everyone to agree 100% with each other. But you can agree with enough topics to prevent a dictatorship.