So wait, if they have a breakthrough with implanting animal hearts into people (and the immune/allergic response to it - they do study these things, since pig hearts would be pretty cheap compared to human ones, and you get a side of bacon along with it), would whacking off be bestiality, too? The blood engorging that member was just through a pig's heart! Extra unclean.
Seriously, they usually cite Genesis 38 (Onan - not the generators), but that story (if not read by a moron) is about betraying family obligations. Pulling out so your sister in law (now wife) doesn't get knocked up, so that you and your own children will inherit. Heck she gets knocked up pretending to be a prostitute with their dad. The punchline at the end of the story is good.http://www.biblegateway.com/passage/?search=Genesis+38&version=NIV
That's TRUE Bible morality!
BTW, 'Pulling out' is not effective birth control, so 'god' killed Onan for the 'thought'. So thinking about masturbation is just as bad as doing it. Best chop your pecker off to be safe!
And if your eye causes you to sin, gouge it out and throw it away. It is better for you to enter life with one eye than to have two eyes and be thrown into the fire of hell.http://bible.cc/matthew/18-9.htm
A 'good Christian' example.http://gawker.com/5845992/man-gouges-out-his-eyes-during-mass