In my opinion, Galante probably had little respect for Rastelli. Lilo was a powerhouse in his day and Rusty was just another soldier when Galante went away. Add to that, Rastelli was on the traitors side of the Bananas war, and being the in the can, it was a situation bound to come to a head.
"Joe Bananas went after Carlo Gambino, the war went on for seven years..... When guys go to the mattresses, they're not out earning" -Tony Soprano
