I think the main difference here is that these are all pre-existing characters, e.g. two of them were in Runaways (a series that I enjoyed). In the case of The Hunger Games, you wouldn't see those characters at all if it wasn't for the story setup. In this case, people already know and like the characters, and this series looks as if it will get in the way of them appearing in future stories.
House to Astonish discussed this in podcast #91 (25m40s-31m17s); they suggested that the book may just have been hideously mis-marketed, which is possible. However, for now I'm assuming that it is what it looks like.
I understand that most stories rely on conflict (particularly in the superhero genre), and I'm ok with that. I've also read some very good stories where characters die. However, this seems different, and I think it's the "audience participation" angle that bothers me the most.
A few months ago, The Onion published a satirical article which claimed to be written by Honey Boo Boo (You Do, Of Course, Realize That This Is Going To End Very, Very Badly). Apparently she's in a reality TV program, although I haven't seen it. The point is, this isn't a wildlife documentary: the act of observation changes the thing being observed.
A few stories have deliberately taken advantage of this. In Sex'n'Death, Martin Clunes' character announces that he will kill himself on live TV unless everyone stops watching, i.e. if the ratings drop to zero. There's a similar idea in Ben Elton's novel Popcorn, where people threaten to shoot their hostages unless everyone stops watching them on TV. Particularly in the former example, I felt slightly uncomfortable about continuing to watch, but I rationalised it by saying that this was just the "show within a show", i.e. the fictional character was talking to a fictional audience rather than to me.
More recently, I read House of Mystery #35. The backup story involved a self-proclaimed sociopath wandering around a shopping mall and talking directly to the reader (i.e. breaking the fourth wall). Here's his theory: "See, you don't want to admit it, but you're essentially just like me. You want these things as badly as I do. You just don't want to get your hands dirty." He has a plan to do some (unspecified) unpleasant things, and asks the reader to help.
"And this is where you come in. You see, I have the singular disadvantage of being a fictional character. I can't set my plan in motion until you turn the page. You could just close the book and walk away. You're practically at the end anyway. But you won't. I know you won't. Because you have to see what happens. So turn it. I know you want to. And you know it too. Let's be honest. Go on. Do it now."
He was right - I did want to know what happened next. In fact, I'm still curious, because that's where I stopped reading, and I haven't bought any of the subsequent issues of that series. At the risk of mangling a physics concept, this seems like "Schrödinger's comic". If I stop reading then the story only exists in potentia, so it's all just hypothetical; the waveform hasn't collapsed into particular events.
That's not a perfect analogy, because the issue has been printed and I'm sure that other people have read it. So, the best time to stop something like this is before it happens. (Long time readers may recognise this logic from my Pinocchio anecdote.)
Back in 1988, DC published Batman: A Death in the Family, where the Joker killed Robin. (More specifically, he killed Jason Todd, the second Robin.) This is significant because they put it to a vote: the second part of the story ended with a cliffhanger, and people could phone a premium rate number to say whether Jason should miraculously survive or die. If he'd survived, he would presumably have been in a hospital bed for the rest of the story, so the creative team could still write/draw most pages of the subsequent issues before the results of the vote came in. The point is that real world actions influenced events within the story.
This all brings me back to Avengers Arena. Simply put, I'm voting with my wallet. I know from experience that comics with low sales get cancelled; it's often happened to titles that I enjoyed reading. So, logically, if enough potential readers can set their curiousity aside and not buy this comic, Marvel will have to cancel it. Hopefully they would put in a happy ending, e.g. "And then Captain America turned up to rescue everyone" rather than "And then the island blew up, killing everyone who was left." If so, that means that all the characters who were due to be killed off in later issues will still be alive, and another writer may be able to use them in a different story.
Granted, most of my friends probably wouldn't be buying this anyway, so I'll just encourage you to keep doing what you're doing.
By way of contrast, here are some other Marvel comics that I do recommend. Firstly, The Thing: Idol of Millions (by Dan Slott). The first few issues involved the same villain as Avengers Arena (Arcade) who brought a group of people to his Murderland. The key difference here is that he gave them a chance:
"As I was saying, this's a game. And for every game, there're rules. On the other side of this island is an 'immunity spot'. Once somebody steps in it ... everybody else has ten seconds to get inside. Do that, and you've won your prize: the island stops tryin' to moirderize ya. If you're outside the area? Well, then you've lost. Work together with your fellow castaways -- or every man for himself, up to you."
So, you have a conflict with external forces (Arcade and his deathtraps). You also have a conflict between members of the group: will they stick together, or betray each other to save themselves? I don't want to give too much away, but suffice it to say some of the characters survived without murdering anyone, and that's really what I want from heroes.
Secondly, Thunderbolts: Faith in Monsters (by Warren Ellis). This is set just after Civil War, so the premise is that all superheroes had to register with the US government; if they didn't, the Thunderbolts (former supervillains) would hunt them down. The unregistered heroes in this storyline were fairly obscure "C list" characters, e.g. The Steel Spider (formerly known as The Spectacular Spider-Kid). Warren Ellis often seems quite cynical, so it would have been easy for him to mock these characters, but he didn't. In fact, he gave a pretty convincing argument for why these people would do what they do. For instance, when Jack Flag saw someone being attacked outside his block of flats, his girlfriend didn't want him to get involved:
"Jack, if you go down there, we'll never be safe. We have to live here too. If you get involved, they'll terrorize us. You know that."
"They're not going to know it's me. That's why we wear masks."
The unregistered heroes didn't all make it through the story unscathed, but at least they stayed true to their principles, and they were fighting against villains rather than each other.