I expect there to be some degree of resistance, but then Clark will be all "Hey, remember the time we were invaded by Thanagar? And the Dominion? And....and....and....? This UP thing will make that a whole less common and if it does happen again we'll have allies we can ask for help." And once he explains it most people will get with the program, with a few vocal detractors like Lex thrown in for spice.
But honestly, what I would actually like to see is a big, hard hit against it from the people. Earth is in the galactic conversation not because our technology or societies have evolved to that level, but because there's a couple dozen god-like beings who happen to call earth home and they are always getting involved in crazy sh*t and pulling the rest of the universe down on our heads. I'd like to see the world go "Yknow what? You guys blew the Source Wall apart. You did this, and this, and this, and it's all come back to bite us regular folks in the ass, so no thanks, we'll pass on the UP."
And then the Golden Age fan in me just wants Clark to say "I dont care."
Now *that* could be a DCU sized shake up.
The heroes on the out's because they're (for once!) doing the responsible thing and taking a long view at the common good.