Homosexual Marriage. Why is the Church picking this battleground ?

[SaintAndrew]

Personally, I don't get why they see homo marriage as something that will change society significantly  more than other moral declines do.

Because society is headed toward the direction of saying the Church's teaching here is hateful and cannot be tolerared. Hate groups aren't given non-profit status, don't get the hospitals licensed, don't get their schools accredited, and generally people who publicly belong to hate groups have trouble making an income. The Church's other teachings can be dismissed by society as antiquarian, but the Church's stance on homosecuality could eventually lead the Church back into the catacombs.   

Applause @ Someone1776.......well said......