The Christian position is to represent God properly and bring him glory (Isaiah 44:3). God tells us to love him (Matthew 22:37) and also to love our neighbor (Matthew 22: 39). However, loving our neighbors does not mean we approve of their sin. True Christians will acknowledge the sinfulness of homosexuality as well as the biblical position that marriage is between a man and a woman.
Furthermore, it is not up to Christians to allow or not allow homosexuals to marry. Christians are not the ones who decide the laws of the land. Different countries have different legal systems, and it is those legal systems that establish parameters of marriage. However, Christians are obligated to stand in opposition to those things which are against God’s word, so they are obligated to stand against homosexual marriage. This opposition can be manifested in different ways such as a verbal declaration, written word, voting, etc.
The secular world disagrees with Christianity and therefore stands in opposition to it in many areas. As secularism gains philosophical influence, social permeation, and more political power, it will eventually persecute those who stand in opposition to its man-centered principles and man-centered morals. This is what happens in secular based governments--just see secularist Russia in the 1900s that killed many millions of Christians.
Anyway, homosexuality is against God’s declared arrangement of marriage. Christians should pray for the redemption of the homosexuals as well as the repentance.