Blizzard has a policy that Guilds shouldn't be based on out of game reasons - so no GBLT guilds, no Christian guilds, no Jewish guilds, no neo-NAZI guilds, no Korean-American guilds, etc.
Blizzard is stuck with the fact that the majority of their player base are homophobic racist assholes, so they try to keep people from making themselves targets.
A better solution would be to ban about 60% of the games player base, but obviously Blizzard doesn't want to lose that sort of money.