I don't think the underground man can come to Christ, at least not as things stand, because I think he is actively participating in the unforgivable sin--that is, a refusal to ask for forgiveness, to turn to God, to humble himself, to repent, to have the courage to be who God wants to make him into. To blaspheme the Holy Ghost is not to denounce him, but to ignore him, to act as though he doesn't exist. Now the underground man is a psychological masochist, he takes pleasure from his own inadequacy and sickness and repulsiveness. He's not palyzed into inaction, he actively chooses it (though he might deny that), he actively chooses to move from idea to idea, activity to activity, because that is what makes him happy.
And this is where he would argue that choosing
inaction is better than any action at all. I know you talk about how he could not come to Christ, and there was a section in the book about that but it was mutilated by the censors. We may never know how he could have faith and still remain underground. What Dostoevsky argues in his later works is that man can come to Christ, but it must be out of their own freedom of choice. We all choose to come to Christ, that is the great freedom God has given us. Maybe I don't necessarily agree that he is refusing forgiveness from God, rather he would argue those that are of a lower consciousness commit acts without thinking about their repercussions, so they may sin but may never acknowledge that sin. And the man of an acute consciousness knows very well his own wickedness and will not do anything that can cause himself to do sin. What the underground man would need to do is break the chains holding him back, as you said from psychological masochism, however in order to do that he cannot be so acute with his consciousness. Unless you change and become like little children, you will never enter the kingdom of heaven.
The underground man is very aware of his own sin and recognizes that by being so vile he cannot go out in the world, lest he cause harm to others and to the world. In a sense you are right, he doesn't recognize that he can be forgiven by God. However not recognizing this forgiveness does paralyze him into the state that he is in. I actually didn't read the work as him taking pleasure into his misery, even-though he is in love with it.
He says at one point that he wish he could be a lazy man, because at least that would be a positive description of him, at least that would be something. But he is something. He is the man that Jn. 3:19-21 speaks of: "And this is the condemnation, that the light has come into the world, and men loved darkness rather than light, because their deeds were evil. For everyone practicing evil hates the light and does not come to the light, lest his deeds should be exposed. But he who does the truth comes to the light, that his deeds may be clearly seen, that they have been done in God."
But does the underground man love darkness over light? He argues that man can be totally in love with suffering (which rejects the utopian ideal) and he is justified by the wickedness he can perpetuate as a human being. It's almost contradictory in a sense because he has high values of man and then he views man as nothing more than dirt in other sections of the book.
People love different shades of darkness and different shades of light. Or rather people love what they believe to be the light when it very well could be steeped in darkness in actuality. The underground man acknowledges what the light is, but he himself cannot come to the light because his darkness was created by his own infatuation with himself. So he rationalizes his own psychological behavior that it's better to be in darkness and do nothing, rather than coming to the light.
But my next question is, what would break him from the darkness? My answer would be to remove the acute consciousness.
Darkness doesn't always have to be overt sin. Sometimes it is that, yes, but more often it is a state of mind. Out of the heart of man comes a thousand horrors. And this is not a man who is merely psychologically trapped in a crappy situation, the way some spousal abuse victims become trapped. This goes far beyond that. And until and unless the underground man is willing to change that, then God can't and won't force him to change for the better. God already gives him the motivation and opportunity to change (Phil. 2:13), but the underground man ignores the call.
But wouldn't the call revert the underground man's thinking at all though? And that goes back to what I raised earlier: "Would it be possible for the Underground Man to leave his state of acute consciousness and return thus back to a state of "ignorant" action? Is there a point in such a higher state of consciousness that would have a man reverse his thinking? "