Pre-approving messages is a terrible idea in every circumstance.
It slows conversations down to crawl. People don’t get the behavioural reward of posting a comment and seeing it appear. That delay is a killer. If you want to kill a community, demand to pre-approve the messages.
The better solution is to pre-approve the people. Only let good people in and remove the bad. If you can’t trust members not to post bad things, then screen them. Only let the best ones in.