Stefan's numbers were at least partially valid. Damon had very little patience, for the most part, and compulsion was an easy way to make them stop whining, or to do what he said, or on occasion to spread their legs without a fight.
"Compulsion is a tool," he said, to both Elena and Stefan.
"Just like a crop, or a collar. I was gifted with the ability, and I don't see why I shouldn't use it when it's needed."