If it is possible to set this, it would halt a lot of the current influx of spam before it starts.

A few of the bots are clever enough to post in existing threads, but much of the spam here are by bots who register then post.

If users were unable to start threads without having at least posted once, these bots would be stopped.

Few non-bots post threads without having posted beforehand, and even for those that do it's hardly much of an inconvenience that they post in reply somewhere else too...