I have been admin on several forums over the years. One thing I have learnt with users, regardless of rules etc there is a "If I can, I will" mentality with some people. Some like to see how far they can push things until they end up on the chopping block.
Putting a forum into moderation mode has two main impacts:
1. The forum is more orderly and harmonious.
2. Overall forum members tend to 'dislike' post moderation, as such it typically (not always) results in a decline of members posting.
At the end of the day, the said owners/admin of the forum have to go with what they feel provides the best outcome for the forum.
The biggest problem with moderation after the post have gone live is the damage is already done, and there are usually a large number of replies following on. Thus the thread can become disjointed (for want of a better term) and hard to follow, as you have gaps in the thread from removing any offending posts.
Whether I, or anyone else likes/dislikes post moderation is really insignificant, the owners/admin are the ones who have to make the call for the better good of all, not just a few.