One thing that the Catholic Church has always been good at instilling is the sense of "Holy Guilt" that I have mentioned in other threads. From an early age, Catholics are taught that some things (venial sins) only cause a blip on the radar of God while other things (mortal sins) cause a total separation from God. Pornography, sex outside of marriage, birth control, gay sex are all viewed as mortal sins or "grave sins."
The teaching is based on the fact that as one delves more and more into porn they begin to not pray or give less and less focus upon the one who is the Creator. They also can begin to numb themselves to human contact and instead replace it with items that take the place of this interaction. 
In the case of sex, the belief is that sex is a gift from God that is designed to procreate the species. It has its roots in Judaic law contained in the First (Old Testament) Covenant. Gay sex does not allow for procreation and is therefore not allowed.
For me, if I really believe that God created me in His image and knew everything about me before I was conceived in the womb...then who was I fooling by looking at porn, erasing it, downloading it, masturbating in the basement, etc. I was only making myself miserable with guilt because I was created gay. I liken it to the thought that I can go and sit in the garage every night of the week and wish I was a car; the fact is I was created as a man. I could go around and wish I was straight but I was created gay. When I accepted that fact, the guilt and other burdens went away and I was happier than I had been in my life. 
I find some gay porn extremely beautiful and erotic; other I don't like. I don't think it has ever gotten out of balance because when I'm in relationships, I really look at porn very little and when I'm not...well...it is useful for teaching, correcting, and rebuking (to steal a line from scripture!)
In some ways it is like alcohol, cigarettes, and many other "isms." When they get out of balance in our life that they consume it, then there is a problem. Some people can handle them and the balance; others can't. But don't beat yourself with the guilt....