I disagree that Vergil holds no blame. First of all, it was because of his selfish desires that he created Urizen. Even if he didn't know what Urizen was going to do, he is at least partially culpable due to people dying at the hands of Urizen.I'm not sure Vergil can actually be blamed for Urizen taking advantage of the tree.
Moreover, it seems obvious that Urizen's actions were never Vergil's plans. He intended to separate the weakness and corruption from himself just to fight Dante, but when Urizen was born he didn't actually care much at all about Dante. Instead he tried to invade and rule over both worlds, something that was explicitly not Vergil's prerogative. It seems as though Vergil had no idea that Urizen would deviate so much from his own desires, and that V trying to stop him is highly indicative of that.
Secondly, I take umbrage with treating Vergil and Urizen separately as individuals. If we're accepting V as Vergil's inner goodness, then I don't see Urizen as anything but Vergil's inner darkness and that on some level, whether consciously or not he did want it and now without any inhibitors to hold him back Urizen could embrace Vergil's evil desires.