It depends on what ideas they all embrace. If they rally around peace and respect, good. If it's rape and pillage they go for, not good.

It is both, potentially. Like minded around what, is the question. There are all sorts of [un]worthy goals and objectives that individuals and groups can pursue and reinforce each other in.

Positives to members regardless of the objective are community and refuge. Negatives can include demands for conformity upon threat of ostracizing, etc.

I try to associate with people who have what I view as positive goals, held for the right reasons.

Community does not preclude diversity. Community can be a diverse group of people seeking and emphasizing commonalities, or they can be a very narrow and non-diverse group circling the wagons around conformity and rigid dogma (religious or otherwise). Communities that encourage diversity and emphasize common cause have the disadvantage relative to less open groups, that they can take forever to reach consensus and can get bogged down in dissent. The unfortunate advantage of more narrow communities is that they obtain agreement and make decisions quickly and generally without a lot of angst.

As long as you do you, I do me and let's strive to do or cause no harm.

Can be both.

If it is a large enough group, I believe eventually it will likely go badly.

Harmful in two ways if the community is made blind and oblivious sheep then they’ll be vulnerable any predator or in this case they’re under the impression that there’s strength in numbers but still easily led to be slaughtered by the ideologies of they believe is leading them.

And the 2nd is if the community is strictly aggressive they’ll easily set off the sheep therefore causing them to react and leave which will eventually lead to these members turning on each other.

If you're referring to this place people are far from like-minded. But if you notice all of the postings where people say that they feel welcome and it makes them feel good, that would make it healthy. Such a place would be harmful if it preaches hate or destruction or violence

In my opinion, it can be both. It can be a means of support and belonging, but if carried too far, it can become the source of group-think, and blind you to other ways of being and thinking.