Eric, it doesn't work that way. You can delete users all you want. Look at the total number there are in this group. You cannot stop them from registering in this system, but you can stop them from becoming active, and thats what I'm doing right now. Also, most of it is BOT activity. They register in, spam, then register in again under a different username, spam, go away, come back and the cycle continues. Deleting users isn't going to help at all, they've already done the damage.
When I put the brakes on activation, you'll notice the spam levels go down to almost zero. One or two will slip through the cracks, but nothing like the last two days.