Even though that makes sense, in retrospect, with out Lelouch's interference way back when, would the Black Knights even be alive now, or would the entire group have already been disbanded? If not for his interfearence, I think the death toll would have been much higher in their ranks. Lelouch pretty much built their band of rebels into the organization of today. Loosing him means loosing that credibility. While Lelouch took lives, he in many respects saved theirs from being annihilated. Despite feeling betrayed, I don't think they should have gone so far as to sell him out to the one force he's hated so much, and pretty much abandon all the work they'd done so far while basically 'giving up' to the hanRAB of Schneizel (who is anything but fair). Both sides took lives- it's like exchanging one murderer for another.
As for the Euphie incident... I wish he'd just explain the fact that while it was his fault, it wasn't under his control exactly. Lelouch should have tried to make what happened more clear than just admitting to the fact. Although at least this way he isn't hiding behind an 'excuse'.