Here’s the key question to my mind. Do Jews have a chiyuv to prevent Goyim from sinning? As Jews we have a chiyuv to admonish other Jews who are over aveirah. SSM is clearly against the Sheva Mitzvos. Do we have the same obligation to admonish Gentiles for violating any of the Sheva Mitzvos?
Let’s take a less emotionally charged issue. The Constitution guarantees the free practice of religion and the U.S. Statutes prohibit discrimination on the basis of religion as well. The Law protects all religions including Hinduism which is clearly Avodas Zora and is also a violation of the Sheva Mitzvos. Are Jews obligated to protest laws protecting said Avodas Zora? Note that the penalty for Avodas Zora and Arayos is the same, both for Jews and Gentiles.