Dean slaughtered four people. They weren't practicing magic, or summoning demons, or otherwise in cahoots with some sort of supernatural double-edge. They were just a bunch of (sleazy) guys. But their sleaziness doesn't matter, not really. And Sam knows that. Even so, their sleaziness is a handhold and hell with moral interrogations, Sam's just like, we're going to table that somewhere very deep and it's going to go away. Okay? Okay. And at least for me, Sam's command of that is the only reason this story kept going.
Sam commands the narrative again for the whole of 10x11, because jesus christ every single time he got on the phone with Dean, shit was going down. XP Like, one undebatable disaster after another. But Sam... just kind of went with it, you know? Which, save for various points at which he put his foot down and actively steered Dean towards this shore or that, has pretty much been how he's dealt with all this so far. This whole last half of S10 (or I guess, also the first half of S10, post-10x03) has essentially been Sam exercising this wildly, crazily free range mentality where Dean is concerned.
I don't mean that in an "oh, Sam is so irresponsible" or "oh, Sam is so negligent" way, either. Because seriously, what else can he really do? (Up until 10x18, that is--what can he really do? and the reason he jumps on the Book of the Damned so fast, well. Perhaps it has something to do with the time sensitivity of his/Dean's problems, but I'd also argue that it wasn't pure impulse. It's not like he hasn't been honing in on this moment for the better part of a year now.) It hasn't been a complete disaster, either. It's not as though Dean hasn't--for the most part, more or less--risen to the occasion.
Whatever its practical efficacy, I think that Sam's means of relating with Dean here (and/or the world at large) is really, really important to him. I think he believes that given the space to swim your own way, and swim and swim and swim--even if it's into dark waters, or hot ones--eventually you can find your way back. No matter what, given the time and the space and the freedom and the trust, you will find your way back.
He desperately needs this to be an actionable truth, both for Dean's sake and his own.
We've determined that Bon Jovi rocks, on occasion. And if all that isn't Livin' on a Prayer, I really don't know what is.
Sorry these are comments-disabled, if that's the kind of thing that irks you. I just don't want to debate, argue, or defend. This is all just between me and Show.