They are hardline Marxist-Leninists, something that is very rare in the western world even amongst those who identify as leftist or socialist. If their views make you uncomfortable, then you're not a ML, which is okay.
Left-wing politics is a very broad spectrum, and a lot of Lemmy users lean towards the more moderate end which brings them into conflict with the more radical communities that are Lemmygrad and Hexbear.
They are defederated from a lot of instances, from their own side or the other's (my instance is defederated from LG and HB defederated itself from my instance)
A correction: Lemmygrad and Hexbear are two different instances, and it's an oversimplification to lump them in together. Lemmygrad does not defederate from any real instance, we have possibly one of the smallest block lists of any bigger instances.