Minor spoilers will follow.
I was recommended to read this arc for it's message. I was warned prior about the large amount of characters present, large amount of dark content, and although I wasn't told about the deus ex machina, it was fairly obvious. None of those things matter though. The plot was only crucial for conveying the message, which is a amped version of the core value of Spiderman. Peter Parker takes the mask and suit because he refuses to stand aside to all the world's abuses, a noble goal for sure. The point of this arc was to test it. People die, it's not shown, but heavily implied. Chaos sets in, people turn on each other, riots fill the streets. The question constantly asked is "What do we do?". Should the heroes chase Carnage to try to stop him sooner, or stay behind and clean up the wake? To many the answer is to chase him, and characters like Cloak and Venom, fueled by a need for vengeance, advocate this.
The truth is that this is the careless choice. While one can pick either and be "right", the morality of a hero should make the choice clear. Spidey staying behind to help is the right choice for two reasons.
1. If he doesn't, those people would die. Emergency services weren't an option, and places like The Deep were collapsing.
2. If he did give chase, what would he do? Every encounter was a skirmish that accomplished nothing. Giving chase would prevent some people from being hurt, but leave others to die. Either way, people would have died, and giving chase so often would have caused more fights, meaning more chances for Carnage to run, and hurt people.
The other piece of the message obviously comes from Spiderman's unwillingness to kill Carnage, because he is a human. This is an idea which is fairly political in retrospect. Basically, the writers put this in, intentionally or not, as a stance on the death penalty. This is not a crackpot assumption, it's pretty damn clear. Despite the crimes committed, Spiderman refuses to see death as an appropriate punishment because of the worth of a human life. No matter the danger, the life must be preserved. It's heavy-handed when viewed in a political light, but there is another angle to view it from. Firestar presents this angle at one point, when she has Carnage at her mercy. She compares her actions to those of The Punisher, stating she isn't that kind of person, who cares more for their own problems and mournings, than those of others.
The idea that I take from this is questioning if people of that type are truly heroes at all. They are willing to sacrifice human life for their perception of right and wrong. To keep this centered on Maximum Carnage, what separates this idea of judgement from those like the Demogoblin, who kills any he perceives to be a "sinner"? Morality is a tricky enough thing without taking the consideration of death as a punishment.
What can be seen through Maximum Carnage is a look at the idea of how to be a hero, in the light of just how much action can be taken by the hero. Should he kill those worthy of it? If so, who determines that, the hero himself? It's not a cut and dried answer, it varies with your views, but the important thing is it makes you think. Because of that, I have to say Maximum Carnage, even for it's fairly weak plot, is something I have to respect for the concepts it presents.