I dont favour deleting posts too much. I can only recall having personally deleting one post, and that was because I gave an answer, and then though that it might have been wrong, so I promptly deleted it and reposted it when I was sure of the answer.
Id much rather see how someones post history evolves over time, than see a recap of the best posts after deleting the nonsense ones or the social reports. I already take enough time as it is to find new people to merit, after checking their post for possible plagiarism, and browsing through their posting history. Id rather not have to add a new task to my KYM (know your merited-to-be), having to second guess the gaps in their posting history.
Besides that, merited posts that later get deleted are a bit of a drag in various ways. Statistically, 6,72% of total overall awarded sMerit is assigned to what is now a deleted post (steeper the first few months than the latter). That is a fair share of traceability that disappears to some extent, and that Id rather not happen either.