I'm going to paste my comment from a similar topic:

I find that conversation flourishes when you limit it to a certain degree. In spaces which are completely open and have a massive range of opinion, what you’ll find is mostly yelling at each other over broad talking points that everyone is already familiar with. After a while, nothing of interest comes out of the far left clashing with the far right all the time. But when you limit it, time can be spent doing other things than yelling at the dickhead on the other side who you have little to no overlap with and see as a dire enemy. You can talk about nuances in principles, differences in organizing, etc. It makes for richer, more interesting conversation.

There's also quite a huge range within the umbrella of leftism, and honestly we already have a huge enough gap there that there's a lot of worthless clashing. Broadening that would only make the site worse.