People will use that to make false acusations to others. Making only members up to X activity will only make it harder to do, but it still going to happen - there are many people with lots of time, or lots of btc to buy accounts
I think a warning system and a waiting time ban(people get 20 min waiting time for some days before getting banned) would be more effective, and less abuse-prone
False accusation is not a problem here. That takes place for reporting a post too. But ultimately it goes to the Mods for filtering out. So, anyone cant ban others only by having multiple high activity accounts.
I like this suggestion of including a waiting time rather than direct ban at first.