But TWOK ended quite optimistically. I really like this aspect of Meyer's work, he seem so militaristic and dark on the first glance but there is always a bright ending and you realize that the guy is not really somebody who is antithetical to Roddenberry. He does the same stuff but, as you said, first everybody has to go through hell.
This usage of contrasts leads to a much more refined notion of paradise and utopia. It is feasible but constantly threatened, you have to strive and fight for it the entire time. Not just out there but also, to use TUC and FC as examples, in yourself. You think you are a nice guy and before you can say Kobayashi Maru you are on record as a racist. But you straighten yourself out before it is too late. Trek can be utterly dark but never cynical.
And what makes you think that the new movie isn't going to end on an upbeat note, like KHAN or TUC or the last movie for that matter? I seem to recall that the 2009 movie ended with Kirk taking command of the ship, the crew working smoothly together, and the Enterprise warping off into space . . . just like the endings of TMP, TUC, etc. Nothing new or cynical about that.
Just because Earth is attacked in the trailer doesn't mean the movie is darker and more cynical than, say, the time the Gorn massacred that colony on Cestus Something. Heck, even the whale probe and V'Ger menaced Earth.
And, personally, I've never thought Trek was supposed to be about "paradise" or "utopia." Things are better in the future, sure, but they aren't perfect and life isn't always easy--especially out on the Final Frontier.
"Risk is our business," remember? And Kirk is many things, but he is not a Boy Scout--or a saint.