okay a few points why not:
1. Message farming: messages you send, even if they get deleted, count towards your total message count.
2. "Latest Posts" list: When you send a message in a thread, it will appear in the "Latest Post" list. to prevent this from happening, there should be a lot of developing, which I think is unnecessary.
3. People can simply think before they post anything. Even if you make a mistake (such as necro-posting by accident (before the necro-post warning got implemented)), it could be removed by asking the staff.
4. It is good to know what things are suggested. I've seen people suggest to edit a thread which people disagreed with in a message like 'nvm', but this is as bad as deleting the thread.
5. Quote message: if you delete your message, people will be confused where some quotes are coming from.
Deleting is a staff feature and right now everything works fine. I don't see a reason to let developers spend time on this feature because of all the problems it comes with. disagree for me
