The point of the roulette system is to fill in groups for old content when someone needs it. The reason you're getting LotA is because there are people who have never done it queuing up for it. The system is doing it's job, in effect. Besides, CT is one of the shortest raids to do, and can be steamrolled pretty quickly. This morning our group ignored skeletons on first boss, killed it with first group on 2nd, etc.

If they let you blacklist LotA, there's going to be a handful of folks that can never find groups to get it done. Thus defeating the purpose of the roulette.