What am I supposed to do?
Because as much as I love John, as much as he needed to tell Dean how proud he was of him, how much he was giving up to save his son's life, in the end he was really passing the responsibility, the duty, and the burden of saving Sam or killing him on to Dean. Because John couldn't do it himself. As often as he was at loggerheads with Sam, even though he knew at least part of what was in store for him if it wasn't somehow averted, when it came down to it he knew he couldn't kill his baby boy if he had to, and he punked out and left that pile of crap for Dean to do. So that "proud of you" has a pretty thick layer of tarnish around the edges for me.