"...would you want Dahmer to go to Hell? Or are you quite happy (assuming that you are an atheist) for him simply to be dead."
Since he's censoring many of my responses, here it is:
I'm not Alex, but I'll answer.
I'm satisfied that Dahmer was imprisoned for the remainder of his life and, unlike some of my liberal friends, I'd have been content to see him put to death by the state (a position that Dahmer is reported to have shared), though I generally oppose capital punishment on the grounds that the legal system isn't structured in such a way that we can satisfactorily prevent unjust executions.
I also wouldn't want to see him tortured, and certainly not forever. I don't think that's justice, it's revenge. He was beaten to death by a fellow inmate and some might consider that justice, but that's a very simplified view of justice that I don't share.
Interestingly, Dahmer is reported to have repented and accepted Christ as his savior. I have no idea if this is true, and neither do you, but it does raise two points:
1. If it is true (and if your religion is true) then any decent Christian should oppose the death penalty and, instead, prefer to give convicts as much time to repent and avoid hell as possible.
2. If it is true (and if your religion is true) then Jeffrey Dahmer is in heaven, right now.
Do you think that's just? Clearly not, as you just used him as an example of someone that you feel most people should want to see sent to Hell.
You also mentioned Hitler. Hitler was, according to his public and private statements a devout Catholic and whether or not you accept that, you must accept that you don't know his 'heart' and aren't his judge, and that it's at least possible that he, too, could have been saved - even if only during his dying breath.
Your religious views have nothing to do with justice because they aren't based on punishing the wicked and rewarding the virtuous. There is no system of merit associated with salvation by grace. To you, salvation is a matter of capriciousness. A death-bed conversion is more valuable to your God than a life spent as a good person.
So, your dichotomy is false on several grounds. As an atheist, I don't have to simply be "quite happy" with the death of a murderer - I can be satisfied with a proper implementation of justice that denies the murderer liberty and, on occasion, life. Also, as an atheist, I never have to rationalize blood lust as justice or be dissatisfied that justice might be overturned by the whim of a divine dictator. I can, instead come to a proper understanding of justice that isn't bound by bronze-age myths.