Er, you raise some good questions.
When we are in power in eretz yisroel, we definitely would judge goyim under halacha; same thing goes when moshiach comes and rules the entire world.
But do we have to risk ourselves to make goyim keep the 7 mitzvos?
We definitely have a responsibility on some level to prevent averos, as per lifnei iver applying to goyim(i can get sources for you on this, but poskim say it regarding doing things which make goyim sin, such as gezel), and supporting those who are declared enemies of Hashem through their abominations would be not nust lifnei iver, but actively helping them commit their atrocities.
But it’s not just for their sake; it’s lesaken olam bemalchus Shakai, creating a world which is as close to ratzon Hashem as possible, which applies to the entire world.
Not only that, but what goyim around us do affects us deeply. We’re influenced by our environment, especially jews who need to work among goyim and who need to go to school, or who are less educated and/or competent in learning Torah; these people will and do fall prey to goyishe society, and they definitely are our responsibility regardless of goyim.
But does that mean we should support, for instance, a neo nazi party if the alternative is the abomination people? That would be likuach nefesh, so no. In such a case, there simply wouldn’t be anyone to support; one’s a spiritual danger and the other is physical – let Hashem decide, it’s shev ve’al taaseh.
But in out case, even the most extreme republicans are not neo nazis. They might be nationalistic, which is never good for us, but there is just as much – if not more – antisemitism on the far left as there is on the far right…but the difference is that the lefties get away with it by dressing it up as antizionism.
So i believe that the metzius is that both would put jews in danger, but even if im wrong, and the maga republicans would present some physical danger; our spiritual health and our mission to make the world in Hashem’s image would take priority. Because trading temporary safety for kovod shomayim is not a good deal.
Now again, that doesn’t mean necessarily that we’d be obligated to fight the abomination people, unless they are making gezeros on us, and we might not be obligated to support the other side, But we definitely would not be able to support the left! That’s clear.
As for historically not being too involved in kiruv, so to speak, there is a machlokes about this. Some say that we shouldn’t reach out to goyim, because we don’t want to give them zchusim, but in this case, when they are destroying society, we’re not giving them zchusim, we’re simply preventing destruction. Remember, no society in history allowed same sex marriage since the mabul, and the medrash rabba says that this was the final straw.
Others, including rav hirsch, say that we are definitely obligated in the spiritual welfare of goyim, but our priority is jews, so until all jews are frum, it’s a moot point.
But that’s regarding kiruv; no one’s saying to go around teaching them about the 7 mitzvos; what we’re saying is not to support those who are actively against those mitzvos.