This seems wasteful since I'd want to just include a summary in my posts, maybe if admins/moderators used bots to make regularly occurring posts or something but even then, most of the time the post content is written by a human.
With that in mind, people who wish to create bots can label their accounts as bots and identify themselves through the user agent when not using an account at all.
The bots don't necessarily have to post/comment, getting rid of all bots doesn't exactly seem productive.