an answer
Why would a supposedly merciful and just God be willing to punish sinners with eternal torment?
I can answer this one! XD It's something I learned in Narra, in the extra Catholic doctrine classes I'd have there, and also in ADMU theo.
...Hell shouldn't be thought of as God punishing people in the sense that "okay you've used up your LAST chance so, I'm offended forever so, I'm going to punish you forever". It's not like God made Hell because He said, "Hey, all the people who hurt me (badly) have to go somewhere." In fact, it would not even be accurate to say that God sends people to Hell.
To make clearer what I'm going to say next, may I use an earthly analogy first? It's pretty certain that death is final, right? Meaning, if somebody you know dies, then you can never, ever talk or communicate to him or her in person, face to face, again. Now, imagine you had a friend who you fought with right before her death. Let's say it was a pretty serious fight--you lost your temper with her, said things hurtful, and parted from her with the determination not to speak to her for a while coz she's just so freaking annoying, stubborn, bullheaded, etc. Let's also say that cool-headedness and the reminder that hey, this girl is my friend doesn't win out for at least the rest of the day. And in an hour she dies, in an instant-death-car-crash thing. Ugly scenario and bad nightmare from some dramatic manga, right? If this had happened to me, I'd feel horrible. I'd be sorry, and want to make up with my friend, but (if we keep this to the earthly level and don't go to the thought that my friend's disembodied now and probably can hear and see all my repentance) I never can make up with her again, never can see her face-to-face and say, please, let's be friends again.
The example had two points: one, death is final for everyone, and two, relationships can be broken pretty seriously. On death, it is final even for God. He can't save you anymore if you die turned away from Him, and you can't do anything to redeem yourself after death, precisely because hey, you're dead.
Going back to the thought that relationships can be broken: if one lives without God, and dies without God, then after death, one is still without God, especially if one never tried or never bothered to look for, much less reconcile, with God during life. Hell is primarily eternal separation from God, as in, totally and completely without God, not as a "withdrawal of love" punishment thing, but as a natural outcome of not having tried to "be friends" with God in the first place.
Why is that so bad? I mean, one can always argue that hey, if I didn't look for God during life, then why should I care if after death, I'm not with Him? Let's use another analogy. You know those sappy love stories when Main Character A doesn't know how much he/she cares for love interest #347 until said #347 gets mortally wounded and is bleeding to death before Main Character A's eyes? Then Main Character A starts losing it and begging #347 not to die, because he/she can't live without #347. It's possible, even in real life. Often we don't realize how important certain (overlooked) people are. And this is the closest to what it is like for a soul that thinks he or she can live without God. I did say I learned this from Catholic doctrine classes, so I hope I am at liberty to insert that this is because man was made for God, to know, love, and serve Him. Man was made to help each other out on earth, too, most definitely. But primarily, man was made for God.
That's the primary aspect of Hell: it's separation from God, eternally, because a man, during his life, chose it to be that way. Does this mean that all who are not Christian will go to Hell? Of course not. It doesn't even mean that all who say there is no God will go to Hell. Catholic doctrine always maintains that we humans cannot judge who will go to eternal damnation, because only God and the person knows all the circumstances and events of that person's life. Heck, God probably knows it better than the person. No one knows how much that person tried to search for the truth, how many opportunities he had to learn it. It's possible that the person never had a chance to explore what is true. However, it is also equally and very, very possible that the person had chances, had the answer right in his face, actually, but just refused to believe. However, no one on earth can tell, because no one on earth knows everything. Catholics never presume to judge if a person goes to Heaven or Hell, because really and truly only God and the person know.
And so, to avoid Hell, what we should do, honestly and fairly, is search for what is true and to understand it as much as we can, bearing in mind first and foremost that it is almost never what we, in our intellectual pride and human density and stupidity, think it is. We should also bear in mind that again, it is possible it is right in front of us, and we just don't want to see it. Forgive me, I can't stress this enough, I see it happen a lot: as a priest once said: humans have this marvelous ability to completely miss the point. It is also possible many feel the need to understand the truth a little more before believing it, and so should keep searching.
(Side note: Sometimes, as "proof" of how rigid the Catholic Church supposedly is, people cite the "fact" that we say those who commit suicide go straight to hell. In the Catholic faith suicide is definitely a grave and mortal sin that would land one in Hell. However, again, nobody would know if firstly, the person knew that suicide was wrong, and secondly, what happened in the last few moments of death. If while jumping off a building, five feet from the ground the suicider realized that what he was doing was wrong and made an act of perfect contrition to God, right then and there, then he would be forgiven, and when he smashed his brains out, would escape Hell. Perfect contrition is something that still has to be defined, though--and I can't do it here, it's going to make things far longer than they already are. XD To end, in the case of suicide, we have to believe in God's mercy, because He is all-merciful, and all-just as well.)
Again, this eternal separation should not be likened to punishment such as being sent to a corner or whipped/flogged/kept prisoner for crimes: it is the result of man's millions of choices during life that eventually made him say, through thought, or word, or even just action, that I do not want to be with God. This is actually the greater loss and pain. ...I wouldn't want to live without somebody I loved very much. I'd feel more horrible if a person died and I only then realized how much I needed him/her. :(
In conclusion: Yes, God is all-merciful, and all-just. He is not "willing to punish sinners with eternal torment", to quote the initial question. " He judges, yes, and proclaims the judgement in his justice; however, He is not saying, "Go away, you hurt me, I hate you." He is not sending the person to Hell on account of personal slight and unlove. He is simply stating what has been true in the life of a person who deserves Hell: "You did not love me in life; therefore even now, you do not love me, and cannot be with me."
“Eternal damnation”...is not attributed to God's initiative because in his merciful love he can only desire the salvation of the beings he created. In reality, it is the creature who closes himself to his love. Damnation consists precisely in definitive separation from God, freely chosen by the human person and confirmed with death that seals his choice for ever. God’s judgement ratifies this state." (John Paul II, General Audience, Wednesday 28 July 1999).
...I hope this made this clearer. Now I have to sleep. If you have any more questions, feel free to comment. XD Goodnight!