I was asked a long time ago whether it bothered me that people would be masturbating to my erotica. My reply was that it would bother me more if they weren't. Good erotica, I explained, is intended to turn us on; plus, as long as it doesn't harm anybody else, it's up to the individual what they do to feel good. The reaction was a shocked one, but hell, I wasn't surprised. If you write erotica and you want the world to be sexually happy, there are bound to be people up in arms about the fact.
I argue it's sexual frustration that does the most harm and a sexually satisfied person (which can include someone whose sole sexual activity is masturbation) is more healthy, balanced and capable of spreading the love than any frustrated individual. I'd urge folks to take responsibility for their desires, perhaps by finding a consenting partner who enjoys the same kind of sex, or by drawing on outlets like erotica or responsible porn.*
My take? If it doesn't harm another, do what you love in this world. That way, you're more capable of caring, helping and expressing. Sexuality counts. And that means sexual health. So my concern isn't whether folks touch themselves when they read my work. It's whether they do so enough.
*I'm not a big specialist on what makes responsible porn, but Violet Blue is wonderful. Check her out here.