I think the problem is that there are many people who would describe themselves as “leftwing” but then propagate neoliberal, conservative or reactionary politics. I’m not 100% aware of all the terms dropped in the post, but in my mind a leftwing community should definitely not include liberals, capitalists or conservatives (these are filtered out above via e.g. liberalism, social democrats, anarcho-capitalists, etc). Imo this rule makes perfect sense.