I have heard the dumbest arguments about onanism from catholics and I would just laugh it off, if it didn't seem to be so common place! Apparently, there are these priests who go around telling people that onanism isn't a mortal sin, unless it is "compulsive." Of course, anything that is "compulsive," is deemed to be beyond your control. Hence the term, "compulsive!" So, the very same priest who says onanism isn't a mortal sin, unless it is "compulsive-onanism," will inevitably say to someone who confesses a "compulsion" to onanism, that since they lack "full control," it isn't a mortal sin either! Thus, onanism is rendered a venial sin, by default!