I can understand why people would like to alter their post. I would like too as well at times but that's not how the site is.
I would think that if it did have an edit feature, people would change their post all the time and it could cause confusion.
I mean, look how many times people will reply to a thread that's over 5 years old without knowing its 5 years old.
If we can't even get that right, then I would hate to see what the edit feature would cause at times.
Perhaps if your post was only editable for 5 minutes before becoming permanent it would be better.
The best advice I can give is to just check your topic/post before you post it.
And if you make a mistake, no big deal. Just learn from it and try to avoid it in the future.