We prevent bad actors from developing (if possible) or having nuclear weapons. If they come to develop it on their own, okay then, however imagine we just gave that technology to everyone?
Nuclear weapons have widespread and massive devastation, the potential energy that builds up with hate is perhaps more terrifying though - as instead of immediately killing millions, you'll have situations like Nazi Germany, and so on - allowing bad actors to gain more and more power and more resources to influence the world.
I don't know and am not saying whether it should be done or not, if a developer who builds something that works with Mastodon's structure should be allowed to build a mechanism in that prevents who they consider bad actors (or bad parents) to having use of their tool; of course the bad actors could copy and develop the tools themselves, however those slight or temporary advantages do play a role in who is a victor - imagine if it was the Nazis had nuclear weapons first.
Generally not aiding people towards their goals who you see are behaving in a way that leads to hate and violence is a good thing, no? Helping them survive, understand, and quell their unrest, yes - but not helping hate and violence boil and explode.
The university Mark Zuckerberg was attending was planning to develop an online version of what they called a physical version of The Facebook. Mark couldn't understand why it was taking them so long and said he could get it launched quickly; the reason it wasn't being launched quickly was the university/committee was trying to understand the security, social, and other implications. Mark didn't care at all about the consequences - including but not limited to him fucking over the twin brothers who hired him to develop ConnectU, leading them on purposefully so he could launch Facebook first. Perhaps if everyone did care about the consequences for what they invest their time and/or money into, then standing for good - rallying good people and helping prop them up as best as we all can all in service to others - would gain a leg up against bad actors, malevolence?