Is masturbation moral or immoral?

[Okay, maybe Mike Johnson is a competent parliamentarian.]

A morally neutral, if somewhat distasteful in some ways, act.

[Okay, maybe Mike Johnson is a competent parliamentarian.]

I'd be interested in hearing a secular argument for the immorality of masturbation, particularly if anyone here actually finds one persuasive.

I can find such religious arguments that aren't Abrahamic pretty easily, but entirely secular arguments may be a bit harder to come by.