It's anti-preaching. What you're seeing here in this scene is a few things and all of them are about what Frank is and what friendship means to him. Frank is beyond friendship. The closest he could come was to allow the little imprisoned bit of his soul that still understands being human to tell Micro to run, before the Bad Thing happens. To run before Frank acts pretty much as he's programmed himself to do. Knowing that Micro's betrayed him is secondary, whether that's because he understands Micro's motives or not. He knows Micro has profited from heroin. That's it now.
Micro is trying to preach while being hopelessly compromised, trying to assume that must not matter to Frank as much as their friendship, because isn't that what humans are like? Remember, the crux of this story is that Micro believes Frank can be saved. Now, it's important he talks like this to Frank. Because it's true, but doesn't matter to Frank; he's considered that already. (There's little you can say to Frank he hasn't probably said to himself, one chilling thing about him; he has, in his mind, nothing to learn from, and therefore does not need, other humans) Because it shows Micro to be human in contrast to Frank, and that's including the somewhat cowardly moments. That's human, that's normal. (If Ennis meant it to be pathetic, he'd let you know, believe me) He's attached to life. And he believes in communication like people normally do. And he feels badly for Frank. He feels, Frank won't allow himself.
Frank doesn't preach, really. Part of his point is that he's mostly done with words. So I think this scene works very well. In fact, I think it's one of Ennis' more memorable with the character.