@crazycells I can see a good use case for this in the sense that chat becomes useful if something doesn't work as intended etc, and you need to speak to an admin or moderator to get it resolved. Certainly something I'd advocate. Fortunately, my experience with NodeBB has been almost 100% positive in the sense of zero issues when signing up etc, but there is always that small percentage who are the exception, and to be able to have some form of communication channel with those users is always preferred in my book.
Unfortunately, there is no easy way to stop a spammer who just registers and keeps DMing people.
And although I mentioned previously about unverified users, these are verified users with legit gmail addresses, so it is hard to stop these ill-intentioned people. I believe the most straightforward solution will be turning on chat functions with moderators all the time for everyone but blocking it for other users until a user gets one reputation or one post. This way, it is effortless to spot spammers since we have the post queue turned on.