If you want, I would be okay with trying a switch to just Asirra for account registration, so long as we keep the UrlStopper extension to block external links from brand-new users. That way no damage can be caused. I could also set up UrlStopper to log events when it is triggered, to confirm whether random user names that registered try to spam. I'm feeling like behavior-based filtering like UrlStopper is really much more effective than "figure out if you're a human" systems can ever be anyway.
I agree. I would never recommend removing that safeguard. Since it has the added benefit of stopping human spammers.