It is not a different standard.
The Church proper does not “vocally discriminate” anyone, regardless of the sin. Not homosexuals, not fornicators, not adulterers, not anti-Catholics, etc. What She does is define sinful behavior, and teach how to maintain proper relationship with God in light of those temptations to act in sin.
Catholics make a public statement about issues such as gay marriage or abortion because they are distinct, tangible issues in the law. I think we have to look at how the founding fathers originally created the laws. Laws were originally made with a more faith-based frame of mind, and chosen based on the practicality of their identification, fair and equitable jurisprudence, and the capacity to enforce them. At the same time, the fathers wanted to ensure that some things were not created on the national level, like a state religion, or state run media, etc. They also did not want to impede on people’s freedoms to choose actions which could not be clearly defined in terms of their morality.
So from all that, we can itemize and analyze individual actions and the legislation (or lack thereof) behind them:
-Murder for example, is clearly immoral…hence illegal.
-Divorce is not so clearly immoral (as it depends on extenuating circumstances beyond the scope of state law)…hence, legal
-Adultery is clearly immoral, but impractical to enforce and to fairly incriminate…hence not illegal.
-Fornication…same as adultery, when it’s done privately. But I do believe that we will see a Catholic voice grow in the area of pornography. It has already begun. As a public display of clear immorality, it is becoming more evident that new laws should be written that render pornography illicit. If porn were prevalent in the late 18th century, I’m certain laws would’ve been written against it. The same goes with many immoral behaviors that simply were not prevalent at that time, but are everywhere today.
-Someone’s capacity to worship as they please is not objectively nor intrinsically immoral, and allowing that worship to include public, peaceful displays of anti-Catholic rhetoric (for example) is necessary to ensure the state does not dictate a person’s freedom to reject God. The law allows for people to worship outside of Christianity because a state religion was to be avoided…because no one’s relationship with the Creator should be forced…they should be free to seek Him as they are moved to…even if that seeking is done ultimately outside of the Christian path…hence, people can freely worship as they please.
-That brings us to gay marriage…immoral because it directly infers the acceptance of same-sex sexual activity…which is clearly immoral. And it distorts the divine element of marriage itself…also an immoral act.
Not a different standard applied to homosexuals…not a different standard applied to the gay-marriage legalization appeal.
The standard is the same…is it immoral?..if so, is it identifiable / able to be fairly incriminated? does it impact societal behavior?..is it practical to enforce? These are the same types of qualifiers aggregately used for all lawmaking (atleast originally). The answers to gay marriage happen to be yes on all counts. These same questions are answered yes on all counts for abortion as well…and Catholics are quite vocal there. Not that gay marriage and abortion are equally immoral…but the standard for judging the legalization is the same.