It would be the gil spammers and SE's inability to effectively make it less obtrusive.

I have to tediously remove more than a dozen blacklisted names every day just so I can add more gil spammers to it. Is thaat the vision SE had when they implemented the blacklist? Someone in an office said "hey, i bet we're gonna get gil spammers, we should make our users block them manually by implemented a blacklist feature"!

I doubt it, I cant use the blacklist as intended to stop communications with someone I don't like, I'm too busy getting whispers and /tell from spammers I could care less about.