The audience knows Angel has his own sins to atone for, but what Angelus did with his body is a separate thing.
The audience certainly knows that argument, but not all of us necessarily agree with it. I won't go quite so far as to say that Angel is nothing more than Angelus with a muzzle, but I WILL say that Angel blames himself for what Angelus did. He has to, otherwise there could be no punishment in forcing a soul and the resulting conscience and sense of guilt on him. Whenever referring to his soulless days, Angel always says "I," not "Angelus." If he can't disassociate himself from his monster, I see no reason to do it for him.
No one DESERVES to lose a loved one, but, as I said earlier, there is definite irony in the fact that Angel, for once, has the opportunity to feel that loss, to feel the rage and desire for vengeance on the perpetrator, and even know what it feels like to have his son basically resurrected with the driving desire to kill him, the same way that we have seen other vampires apparently instinctive desire to kill their human families.
Something else to consider, however, is that, as we all agree, Angel doesn't DESERVE to lose Connor, doing so is a definite learning experience for him, and as such, has the potential to strengthen his determination to seek whatever degree of redemption that he might one day attain.
