The first would be because Historically a couple that wanted to live together got married so they would not be "living in sin". So would that change for a homosexual couple?
Also #30 goes changes the promiscuity angle. If the very premise of Holy Matrimony is violated by the nature of homosexual marriage, then would infidelity really violate the "holy" marriage?
Read a few verses beginning at both Mark 10:6 and Matthew 19:4, it is GOD’s teaching on...marriage.