Although marriage laws are necessarily local in nature, the Catholic Church is an organization with world-wide power, influence, and connections. It represents a tremendous amount of potential social, political, and moral pressure. Catholic leaders have also made common cause with other religious organizations which oppose gay marriage for similar reasons - conservative evangelical Christians in America, for example. Does this mean that they will be successful?
Actually, there isn't much evidence that the church is succeeding. Catholic politicians everywhere have been told to fight gay marriage, but they either refuse to do so or, when they do, their position isn't strong enough to make much headway. The results in the battle against gay marriage are not unlike the results in the Catholic Church's efforts against divorce or abortion.
The legalization of gay marriage is spreading around the world. In Canada same-sex couples can marry in Ontario, British Columbia, and Quebec. The Netherlands has full marriage and registered partnership rights for both same sex and opposite sex couples. Belgium provides full marriage (but not adoption) rights to gay and lesbian couples. Denmark, Germany, France, and Portugal have registered partnerships for gays that provide all or at least many the same rights as marriage and Spain has plans to join them.
Even though the quest for full legal marriage for gays will take a while in most places and will entail a difficult, winding road, it seems unlikely that the Roman Catholic Church has much of a chance to really reverse things. I don't foresee gay marriage becoming illegal in places like the Netherlands or Belgium. Anything is possible, that is true, but Catholic leaders will need to face the fact that western society is simply moving past them, just as it did with issues like divorce.
One of the reasons for this is the fact that fewer and fewer people today accept the natural law arguments used by the Catholic Church to oppose gay marriage. People no longer consider procreation the necessary and intrinsic purpose of either sex or marriage; because of this, they simply aren't likely to start believing that things such as contraception or gay marriage are "intrinsically" evil or disordered. There is no prospect for getting people to change their minds and the Catholic church has lost the fight.
Perhaps some Catholic leaders are realizing this and trying to find ways to deal with it. Monsignor Manuel Monteiro de Castro, papal envoy to Spain, has spoken out in favor of some sort of legal recognition for same-sex couples. He doesn't think that they should be considered marriage, but he does think that the church's position here should move forward. According to Castro, "They are not the same as marriage. We will leave the term marriage for that which it has always referred to, and other arrangements should be given other names."
This contradicts what the pope has said and I can only imagine what sort of conversations the above comments generated within the Vatican. It's nice, however, to see that someone with such a position has been thinking about how and why the Roman Catholic Church should change. It demonstrates that there is at least a little hope, assuming of course that people like Castro aren't shoved out of power entirely because of their comments.
The ability to change is even more evident among Catholic laity. Most of the lawmakers in Massachusetts are Catholic, but most of them voted not to amend the state Constitution in order to ban gay marriage. That was the right decision because no matter how they feel personally about whether gays should marry, it is undeniable that gay marriage should not be banned simply because some religious groups consider it sacrilegious. The legal institution of marriage should not and cannot be defined by the doctrines of certain religious groups and a fair number of Catholic politicians both in America and Europe seem to realize this.