Your overlap comments are attempting to make all things equal and they aren't. Some groups have very little overlap, others have a lot. If you don't see why white supremacists would overlap with white nationalists...well. Is that what you are saying?
KKK - Socialist -> Bullshit. You can't substantiate that.
One can be a nationalist and not promote racism - agreed. But I'm going to insist on knowing what qualifier comes before nationalist then. German? Irish? You can't just be a nationalist, because that isn't what nationalist means.
You make the case for American Nationalism, but I'd want to make really sure that anyone using that label meant the same thing I meant. And that is the danger of words without context. Lokaire said white nationalists are Caucasian patriots, and you seem to agree with me that when people say white nationalist they mean something that isn't' that. So, when people say they are a nationalist...I mean I would personally stay away from the word and just stick with patriot, but if I insisted on sticking with it, I'd be ready to say why.
America First...similar in that you can be for America first in the same way that you pay your bills before helping out family - it isn't selfish to take care of your own basic needs. But like nationalist groups, xenophobes and racists can sneak in and try to steer that ship in their direction because there is overlap in goals there, if not in the reasons for those goals.
I would point out one thing: the money we give other countries isn't selfless. We are promoting American interests. We give more than other countries to groups like NATO and WHO, but we expect to have more say in those groups policies as well. The current pandemic should show why giving to the WHO is important. I get that they could have handled COVID better, but you don't get rid of the fire department because a house burned down - you fix the fire department. Seriously - we don't give money away unless we are getting something. You could make the case that we should mind our own business, but the last time we had an America First policy was leading up to WWII and we ended up changing our minds.