[joshfraser]

Your blacklist becomes someone else's favorites list.

Changing a single byte changes the entire hash, so blacklists aren't a great solution if censorship is what you're after.

[atrus]

Blacklists are double hashed, so they aren't useful for finding 'bad' content.

[tscs37]

And who can assure that these blacklists won't be manipulated for someone's gain? Ie, surpressing activity they don't like on the network?