How is there any down side to it? Actually, there is also Legitimate Gambling in SWTOR's Game Update 2.8 (just implemented)
1. It's a fun gold sink ( and man do we need a fun gold sink)
2. You kill things in Wow all the time, oh noes but we cannot have gambling!
3. You can hear every vile thing known to man in trade chat, but I guess gambling is too fucking crazy!
4. It would really add another dimension to the game especially during down times (between raids or whatever)
5. I do believe there would be a general and wide interest in it
Once the Debbie-downers have their say here, I think weed that out and really consider how fun this could be.