I could see that as maybe an option?
Talking strictly about MU out of the box, email validation is the only small defense that keeps "some" spammers out.
Plus, it lets me know that if I need to contact a user, that their contact information is legitimate.
I could see taking out the validation key, perhaps, but at least send the username/pass to their email.
On the other hand, if you were to add in an approval system for signups (as an option), that might help too.
Heck, how about coding in an optional captcha, simple question, or some other type of intervention as further options?
/me... I hate spammers. With a captcha and the email validation, the only spammers I get are the "noob" spammers that are dumb enough to sit there and actually manually input their stuff.
Sure, there are a few people that seem to be having trouble with it, but it's more on their host side, and the fact that they just don't really have the skills to properly setup an MU environment.
Optional, maybe. Removal: please don't.