Thats not entirely true, many people who bot are also very active players when they DON'T bot. It's pretty common to bot from work for example, and not add much more than numbers to the game, as you say, but the same player can be very active, social and a good RP'er when at the computer on nights and weekends. Very few players, if any, are 100% bots. So just wiping them from the game does not only remove a number.
I'd much more prefer they DONT play at all though if all they can do is bot, and keep playing actively when they can. Unfortunately the rewards for botting are so good, people do it anyway. We basically offer a bank vault full of gold, without any security, and then hoping to catch and punish the people who can't help but rob it all the time... It's not a perfect setup, but it's what we got to work with currently.