Sure you do...it's called a 'first draft'.
Perhaps a better analogy would be conversation. You can jump into the flow, and later regret what you said. Forums are weird because in one sense they are like conversation...dynamic...a stream with a flow. And on the other hand, once written, words are permanent, static markers...a record.
Plenty of times I have tried to be thoughtful, or precise, and afterwards realized that I conveyed other meaning.
Don't take away my editing timeframe!
When you hand in an essay for school or a report for work you dont get to edit it after you hand it in.