Marriage is defined, instituted, and upheld by God, not man. As such, if any allowances are made against the original intent, then it needs to come from God, such as God permitting divorce under the Law of Moses. Likewise, any recovery of the original intent also must come from God, which is what Christ did during His ministry, as recorded in Matthew 19. Further, since God holds all authority on this matter, man can only govern it by authority granted from God and should be carried out in accordance with God’s design and decree. The Church, Christ’s bride, is the only one God has granted this authority to.
Now, it is entirely possible for marriages among Hindus and Muslims to be considered valid. In fact, I’m reasonably certain that the Church considers them valid unless proven otherwise, and should the couple divorce and remarry, they would require an annulment from the Church should they desire to become Catholic. However, these marriages still have to follow the actual definition and institution of marriage, and part of that is being between a man and woman, as Christ Himself taught.
The problem with equating a marriage between two men and a Muslim marriage between a man and a woman is that the Muslim marriage follows God’s design about who can marry. The marriage between two men is contrary to the definition of marriage given by God. Therefore, it can’t be considered valid before God, regardless of what governments say, because they don’t have authority to define or govern it in that regard.
Now, even if we theoretically can support political movements to give heterosexual and homosexual couples equal rights (I’m not 100% of the Church’s stance on that), we shouldn’t fall into the trap of acting like the government holds any authority in what marriage actually is or acting like marriage is just some definition different groups come up with.
