"Superman" has been going liberal-activist for a while. Before John Byrne took over, Superman was anti-gun and the problem isn't the tool, it's the idiots misusing the tool. But the blame is on the gun, and the "possession" that guns have over people in their lefty minds. It's been a long, slow descent. That's why once they killed off the original Superman in such a cheesy way and then brought him back as an evil Black Lantern, I was done.
Ever since Time Warner bought DC Comics, they've gone downhill. The art has not been what it once was, the storylines stink, and darned near every major hero gets "rebooted" every few years. Between Identity Crisis, Infinite Crisis and that other goofy crisis that DC Comics creates, more confusion and continuity issues ensue. DC Comics' sales have not been all that good in the last decade and they are desperate. This is just more drama out of the Time Warner folks who took over DC Comics. They're destroying DC Comics. DC's gone uber-liberal and I had to say enough's enough.
I knew something was wrong when DC stopped publishing their "Letters" pages. It meant they weren't going to listen to readers any more. So readers voted with their wallets.
Actually, having now read the story in question, there's nothing "uber-liberal" about it, unless you consider Superman participating in a protest against the Iranian government to be "uber-liberal". That was the whole point of Superman renouncing his citizenship, you can't have a big ol' representative of America stepping on toes throughout the world without serious reprisal against the American people.
Besides, the way secret identities work, I'm sure Clark Kent will be more than happy to vote in the next US election. Just don't expect him to be gung-ho against illegal immigration, all things considered (well, at least not unless J.M. Straczinski's writing for him, but JMS stories have a way of 'disappearing' from the continuity of whatever character he's tackled recently as soon as he leaves the title. Really, the comic companies would be better off paying him his money and throwing the script in the trash than waste printing costs).
(I hope you don't mind me fixing the tags there, so others know who's saying what)
To a certain extent Superman has been a "liberal activist" since his inception. This shouldn't be too surprising, comic book writers have always been a fairly liberal lot (save Ditko, who was an Objectivist Libertarian, and the only Objectivist Libertarian to ever produce art worthy of consumption. Yeah, Ayn Rand, Terry Goodkind I'm talking about you!). If you're going to base your reading of comics on political views, you're pretty much stuck with Frank Miller and that guy who writes "Pigman" or whatever it's called.
As for killing off the "original" Superman, I'm assuming you mean Earth-2 Superman. Yeah, that was pretty cheesy, and reading any Secret Crisis Crossover Infinity War deal from either of the Big Two (DC and Marvel, that is) is guaranteed to rot your brains (save World War Hulk. I highly recommend it, 7 issues of Hulk smashing glee). Stick with the monthlies of your favorite characters (or even better the trade paperbacks of story-lines you know are good). But don't write off an entire comic company due to the mistakes of one company-wide crossover, at the most write off the writer (I refuse to read anything by Mark Millar after he came out as Pro-registration in the Civil War story on the Marvel end).