Well the first thing to understand is that they're statists, and all statists are authoritarians by default. Every state seeks to preserve itself and so every state will use authority when it is faced with potential destruction. This is not inherently a bad thing, it obviously depends on the government in question, and who is trying to destroy it, and why. Obviously I as a socialist defend the use of authority to protect the continued existence a socialist state. Liberals tend to always justify the use of authoritarian means used by whoever they support, and then they are intellectually dishonest and pretend that somehow their use of authority isn't "authoritarian".

Additionally, democracy itself is authoritarian. It is the means by which the democratic will of the people express its authority, by means of force. What happens if someone picks up a gun and tries to oppose the democratic consensus? Do you just sit by and let the democracy be destroyed? No, the democratic state uses its own authority to oppress the opposition.

There is no such thing as a distinction between "democracy" and "authoritarian". It's a meaningless buzzword. The opposite of a democracy is an autocracy or an oligarchy, not "authoritarian". The use of this word in modern day political discourse is just something westerners fling at other people's democracies they don't like for daring to vote for something against US interests and want to see them blown up and millions killed and displaced.

I'm not sure if I need to get into the record of liberals on war. Both world wars, and the history of almost every war in the last hundred years not involving a socialist state. There's also the question of the massive ideological mass murders liberals have carried out, but that's a much bigger issue explored in things like The Jakarta Method, which I warn you is really really horrific reading.