Soulless Sam has no feelings. But he remembers having feelings. Vividly. My memory of the end of You Can’t Handle the Truth is that the idea that he can’t feel, that he doesn’t actually care about Lisa and Ben, that he doesn’t get scared anymore, that idea still stuns him. Even though it’s been more than a year.
Soulless Sam never outright says why he wants his soul back. When discussing him, fans sometimes even forget that he did want it back initially. Dean never asks why. Here is what Sam does say: “I don't know if how I am is better or worse. It's different. You get the job done, and nothing really hurts. That's not the worst thing. But I've been thinking. And it was... it was kinda harder. But there are also things about it I remember that I... Let's just say I think I should probably go back to being him.”
My current thought about Sam, both souled and unsouled, is that he’s very analytical. He's kind of disconnected from his emotions. It's not that he thinks they’re not there or that he’s better than them. He knows perfectly well that his emotions influence him in many positive and negative ways. But someone on tumblr once pointed out to me that if it was Dean in Sam, Interrupted, he would have known exactly why he was angry, not found it bewildering. Dean is less self-analytical, but he’s more self-aware. More connected to himself. Sam is more distant from his emotions. It’s not that he’s not emotional - souled Sam is very emotional. But he can’t always see what he’s feeling, or why.
And soulless Sam is almost unaware of his lack of emotions. He’s been soulless for over a year, and it’s still new to him. Maybe he couldn’t even articulate what it is that he remembers about being his souled self, whatever it is that makes him want to return to what he was.
In Exile on Main Street, soulless Sam and Dean have this exchange:
Sam: I guess I just, wish you were coming, that's all.
Sam: Don't be stupid
Dean: No, I mean it. I mean, you know plenty of good hunters. I'm rusty. I did something seriously stupid going out there. I almost got us both killed.
Sam: And that's exactly why I want you.
Dean: What are you talking about?
Sam: You just went. You didn't hesitate. Because you care, and that's who you are. Me? I wouldn't even think to try.
Dean: Yes, you would.
Sam: No, Dean. I'm telling you, it's just better with you around. That's all.
I think Sam is being sincere about Dean caring, and that this is why he wants Dean. It’s not that Sam cares about Dean - he doesn’t. But we know, from what he says in All Dogs Go to Heaven, and from his behavior, that he wants to care. He remembers how much he loved Dean. He remembers what it meant to him.
He’s not willing to die, in order to care. He doesn’t care about caring THAT much. He wants to care, but it doesn’t mean a huge amount to him. Nothing does.
I like soulless, but not as much as souled Sam. Soulless has many of souled’s traits, but he’s lacking souled Sam’s passion and compassion, and those are two things about Sam that I truly love.