When I read the title to this topic, I was reminded of this article I read on THE BEAT:
http://pwbeat.publishersweekly.com/blog/2007/10/26/would-cheering-up-sell-more-comics/
Which had a link to a ICv2 article here:
http://www.icv2.com/articles/talkback/11521.html
It addresses the ancedote of comic shop owner John Riley who surmises that comic book sales may be decreasing, or at least would be better, if they, and Marvel is used as the example in the above article, wasn't as grim as the world around us currently is. The case is made that comics, even Marvel, used to offer a sort of escapism even as it took the babysteps of commenting on then-current things like Communism, the Cold War, Racism, and Vietnam.
Basically the point of the articles was that Marvel, and mainstream superhero comics in general, have gotten too dark and morally ambigous and with those themes already oozing throughout society, they don't offer any escapism, and also seemingly aren't colorful enough to attract kids or others not affiliated with comics. (Examples are given of kids seeming to catch their eye on brighter Silver Age comics rather than contempory covers/books)
Personally, while I feel these articles have a fair point, it is worth noting that Marvel's events have scored great sales for the post-1994 era of comics even WITH seeming to be dark or commenting on the grim times. The death of Captain America, which had all sorts of hintings of civil rights stuff, political assasinations like JFK, and a divided nation, sold almost a half million copies alone (and that was just the first print). Any comic book that tries to be light-hearted or offer non-commentary escapism sinks like a stone in the Top 100 list; just ask Robert Kirkman, who has had several books die that way (as has Dan Slott). So to me this is a sort of "chicken or egg" sort of thing. Would Marvel & DC be having infighting heroes, more gore/political commentary, or even deaths if their audiences didn't support said stories with good sales? CIVIL WAR was a monster hit for Marvel in terms of sales. WORLD WAR HULK, offering a more straight-forward comic book story, isn't making CW numbers. So, obviously, part of this is playing to the crowd.
I mean if DC's IDENTITY CRISIS, which arguably restarted that trend back into grimness & divided, morally challenged heroics, hadn't sold as well as it did, despite various reprintings, we wouldn't be here now. So do you blame the companies for writing them, or the fans for supporting many of these stories while letting lighter books like THE THING or MARVEL TEAM-UP hit the dust?