1) Overturning 2,000 year old traditions that are the foundation stones of all civilized society would be a societal disaster. Traditions evolve for a reason and the father/mother, man/women partnership is THE fundemental building block of society. We should be doing everything practical to strengthen traditional marriage and certainly nothing to weaken it.
2) Homos are more promiscuous than rabbits/minks. The most promiscuous hetero comes no where near the number of partners in any given time period that the average homo does. Even so-called "committed" couples very often invite over-night guests into their relationship. Marriage under these circumstances devolves merely into a convenient method for attaining societal freebies like health insurance, paid leave, and other benies that society typically provides to man & wife.
3) Anal intercourse is the most unhealthy practice on the planet. Its more dangerous than smoking, drinking, or drug addiction. Even if one discounts AIDS, the transfer of STDs (see 2 above) in the homo community dwarfs anything in the hetero community. And its not merely STDs, as if that weren't enough, but colon cancer and diseases carried in fecal matter are rampant in the homo community. How can any practice that is so inherently unhealthy be considered normal?
For these reasons homo activity can never be placed upon the same plain as traditional man/woman relationships. That we are even having to point out this obvious truth reflects the level of damage that moral relativism has had on our sex-saturated society.
Here then is the reason that Holy Scripture so clearly warns against these deadly practices; we ignore them at our own peril.
What I find interesting is that, to my knowledge, there is no major culture (perhaps none at all) in the world where homosexuality is treated as a normal and acceptable lifestyle. If one exists, I'd like to know (and not some minor blip in the corner of a small island, either).