Board Thread:General Discussion/@comment-26412219-20150803161431/@comment-24674051-20150804152558

There's 2 different things going on.

First, the blame for a specific action, such as casting the DC, has to lie with the person that does the deed. Regina the first time, and Snow the second time. Rumple is to blame for his manipulations, but the people he manipulated are to blame for allowing themselves to be manipulated.

Now, the other side is the whatI would call the Domino effect. Specifically, each action taken by one person led to another action by a different person. For example. Zoso Manipulating Rumple into killing him (which is what he did) led to Rumple having the Dark One curse, which led to him alienating his son to the point of running away, which led Rumple to find the Dark Curse, which led to corrupting and manipulating Regina into casting the curse, and so on. I would not call that blame necessarily, but more just Cause and Effect. And in these type of situations, it's not a matter of assigning blame, but figuring out how to break the chain.

Emma choosing to tether the darkness to herself was her decision (and therefore her fault), but that was just the current end to a very long sequence of events going back to Merlin and whoever chose to be the First Dark One. (and maybe even before that, who knows where the beginning of the chain is.)