A large part of this problem can easily be solved:
Remove grenades from multiplayer.
They're very rarely used correctly anyway, and it'll leave the griefers with a much less satisfying way of being a ****, opening and closing doors. Alternatively, make the grenades cost 3,000 plus. That way, griefers have to do a hell of a lot of work/waiting to earn that single chance of pissing everyone off, before they're ultimately kicked and faced with another slow, uphill climb.
However, with how long simple stuff like the Nomad gate bug has been around, I'm pretty much convinced the developers took their money and ran.