I see a hivemind as unthinking conformity. The way you avoid an unthinking hivemind is by harnessing the power of group dynamics to push against unthinking conformity such that refusal to be an unthinking conformist is the group norm.

I don't think unthinking conformity is the norm on HN. Thus, I don't think it has a hivemind.

Certainly, there are group norms of some sort here. There are always group norms.

But some group norms are healthier than others. In my opinion, those that push back against unthinking conformity are better than those that push towards it.