Thread about masturbation becomes thread about grammar. Only on the SDMB. 
Re: the OP, I’m afraid I have nothing to add, being neither female nor Catholic, but I couldn’t resist saying that.
WooHoooo! I’m grammarcating like a motherfuck!
(genuflect, genuflect, genuflect.)
Of course, a thread that’s about grammar from the beginning is, by definition, already masturbatory. 
Accidence will happen. 
Somewhere I still have B.C. comic strip from 20+ years ago (when it was still funny).
B.C. reads from book sitting on a rock, “Go forth and multiply.”
He then says: “I don’t even know what I’m doing, and I’m batting cleanup?”
Ba-da-boom, ba-da-bing. 
Hey! Leave my grammar out of this. She’s a sweet old lady who’d never do anything like that.
What?
And penis will ensue.
Does that bring us back onto topic? Or does clitoris need to ensue, as well?
I’ve always suspected, in my more cynical moods, that the Church uses guilt to keep people in line. It would work like this:
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Label a behaviour as sinful.
It’s got to be something everybody does, yet everybody must think they’re the only ones doing it.
Masturbating, or dirty thoughts, works the purpose just fine. It is done in private and every man thinks he’s the only one who does it. Or, the only one who does it that much. That still applies, even in these modern times. Most of my boyfriends thought they masturbated more then the average guy, and were slightly ashamed of it. -
When everybody thinks they’ve got something to be ashamed of, they are easier to be kept in line. Divide 'em and rule 'em. When a guy is singled out for “impurity”, no-one will come to his defense, because everybody feels they’ve got something to hide too and nobody wants to draw attention to their own secretly sinful selves.
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The mechanism further perpetuates itself because those who “sin” will try to make up for sinning by fiercely condemning “sinning” in others.
The Church has done this for ages, with, I daresay, results the opposite of what they say they want to achieve. Making sex sinful ensures it has a foremost place in everybody’s minds. It’s basically the “you must not, not think of a purple elephant”-paradox.
Making sex a dirty secret ensures people won’t get informed well, and won’t report abuse.
What’s the region with the lowest rate of teenage pregnancy in the world? A devoutly Roman-catholic country? The USA-Bible-belt? No! It used to be the Netherlands, with its totally permissive, practical young-people-will-do-it-anyway so-here’s-your-contraceptive-and-here’s-how-you-use-it-and-have-fun-now-dears-attitude.
It is interesting that the church on the whole is silent on female masturbation. If my theory of control is right, female masturbation wouldn’t be an issue precisely because many women (about 30 %) aren’t interested in masturbating, so they canot be made feel guilty about something they just don’t do.
Instead, women are/were kept in line because they had to worry about their sexual reputation (even more then their actual behavior). A reputation is a very fragile thing, easily damaged by even such innocent behaviour as talking to a guy or looking at him too long. (which is something every girl will do). The fear of being called a “slut” keeps women divided and subdued in much the same way as men can be kept in line by condemning masturbation and sexual thoughts.
I’m not understanding why the Church is being called silent on female masturbation when I believe “deliberate stimulation of the genital organs in order to derive sexual pleasure” would apply equally?