I was referring to the commonly understood definition as masturbation, though also including other forms of onanism as well. I think the form of onanism called masturbation is the gateway drug to societal decay.
Well, it could be. It is a mortal sin, practically all males commit it at one time or another in their lives, many if not most women do the same, it is a very difficult habit to break once indulged in, hardly anyone thinks it is a sin, and none of those people will ever repent of it. Many people go straight from masturbation to contraceptive sex-on-demand, and never in their lives
learn the virtue of sexual self-control and abstinence.
Put another way, how many people in our time say to themselves "I am going to have to sacrifice any physical sexual expression for a number of years, possibly even for a lifetime, no matter how badly I want it, nor how strong the urge might be"?