The male and the female reproductive systems were naturally or supernaturally designed to compliment each other. Each contributes something that the other does not have in order to make them, both working together, a complete whole. Unlike the digestive system, the respiratory system and other systems of the body which are complete within themselves and will do all that they were designed (naturally or supernaturally) to do without influence or assistance from anyone or anything, neither the male nor the female reproductive system has the capacity to do all that it was designed to do without the benefit of the other. And, the use of either without the other in any way - shape, form or fashion - is un-natural, abnormal and downright disgusting.
Semen is not waste, nor is it the byproduct of a sick thrill and serves no purpose in either end of the digestive tract of any individual - male or female. It has a very specific purpose in life and that purpose can only be fulfilled in the reproductive system of a sexually mature female of the same species as the donor, and... there are no substitutes!
Less intelligent life forms have instincts that dictate their behavior. And, while they may or may not have any idea why they do what they do, when it comes to taking care of natures business, they tend to always get it right - male to female - without exception. Humans, on the other hand, with no instincts are gifted with the ability to choose and quite often make the wrong choice.
Choice? Yes, choice. The reproductive system is a system that we can live without. And, if we can live without the reproductive system then obviously we can live without sex (any kind of sex). However, if we choose not to then that my friends is called a choice and, sexual choices like all other choices are made not by the reproductive system but by the brain. That an individual with a healthy and fully functional reproductive system is incapable of achieving sexual harmony with a member of the opposite sex is not a matter of being but a state of mind. Homosexual behavior does not make one a particular kind of being. It makes one a being with a particular kind of behavior.
No, I am not homophobic and I couldn't care less what two (or more) consenting adults do to, for or with each other. If you want to love each other and live together in some weird union, go right ahead. If you want to marry each other go to Massachusetts (it would be nice if you'd stay there).
Do whatever you like, just stop trying to deceive normal minds into accepting abnormal behavior as if it's not a choice. And whatever you do leave the children out of this. You can't have 'em - you don't need 'em.