Valachi was the one who said that Scalise was killed due to him (and Anastasia) selling memberships. That´s a theory I don´t hold much stock into. Sounds wierd that bosses would do something despicable like that. It goes against all the rules of what a man of honor should abide to. However, it may have been used as a false excuse to kill him. Another theory is that Scalise grew too powerful and that Anastasia therefore feared him. But this holds no water either because Anastasia could easily have gotten rid of the problem simply by demoting him. In fact, killing him would have increased the problem if Scalise had a large faction behind him. A third theory is Scalises´s alleged involvment with drugs. It is said that Scalise was behind a big heroin deal that went sour and that investors lost a lot of money. It could also be that Anastasia was unaware of Scalise´s involvment and decided to whack him when he found out. And of course, there is also the Costello connection. Who knows...perhaps Scalise had knowledge of the assassination attempt on Costello (who was very tight with Anastasia) but never informed Anastasia about it?