What’s not to understand about how Jimmy Akin explained it? My analogy is if a fire is already going, and it’s not currently possible to put it out at least try to take steps to lessen the damage it can cause and keep it from getting worse until the time comes when it is possible to put it completely out.
I agree with Tigg " I think I prefer doctrinal purity."
Having said that, the Catholic Church presumes that marriages between a man and woman are valid unless proven otherwise, even the marriages of non Catholics and non Christians. They have valid natural marriages. That is not possible for 2 men or two women.
The CCC says that homosexuality is disordered and homosexuals are called to chastity
2357 Homosexuality refers to relations between men or between women who experience an exclusive or predominant sexual attraction toward persons of the same sex. It has taken a great variety of forms through the centuries and in different cultures. Its psychological genesis remains largely unexplained. **Basing itself on Sacred Scripture, which presents homosexual acts as acts of grave depravity,140 tradition has always declared that "homosexual acts are intrinsically disordered."141 They are contrary to the natural law. **They close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity.
Under no circumstances can they be approved.
2358 The number of men and women who have deep-seated homosexual tendencies is not negligible. This inclination, which is objectively disordered, constitutes for most of them a trial. They must be accepted with respect, compassion, and sensitivity. Every sign of unjust discrimination in their regard should be avoided. These persons are called to fulfill God’s will in their lives and, if they are Christians, to unite to the sacrifice of the Lord’s Cross the difficulties they may encounter from their condition.
2359
Homosexual persons are called to chastity. By the virtues of self-mastery that teach them inner freedom, at times by the support of disinterested friendship, by prayer and sacramental grace, they can and should gradually and resolutely approach Christian perfection.
Supporting same sex civil unions is certainly not a way to slow the spread, it does the opposite and by lending an air of legitimacy.