There are surely some decent people on Hexbear, the problem is that there are a lot that are not, and many have explicitly stated that they want to disrupt other instances. And the final nail in the coffin is IMHO that the admins on Hexbear have explicitly stated that they will not moderate their users for things they do on other instances (making the “be a good neighbor” part in their original announcement a fig leaf at best).
The entire point of decentralized moderation in the fediverse is that instances are responsible for their member’s conduct on other instances. Any instance that explicitly violates this (as Hexbear admins openly say) needs to be defederated as they actively harm the network.