The left are immature thinkers. They cannot follow a thought through to its logical conclusion so as to critically evaluate it. They prefer to use emotion, which they conclude makes them good & caring. Example: Sweden + open borders = muslim hellhole = imminent civil war.
They believe in equality of outcome not equality of opportunity. To attempt to achieve that, the State needs to have immense control. The left likes that very much. Big controlling state is good. Collectivism is good. Freedom & true diversity (that of ideas) is a threat to that.
That is why the left have to censor & silence alternative ideas. If you force them to think things through to their logical conclusion, they lose. Because their arguments are ridiculous. They are forced to confront reality rather than the way they insist reality should be.