I also wonder if the shadow may contain a person’s dark side. Ripping the shadow from his enemies leaves them too meek and passive to take any action against him, but concentrating all that darkness eventually makes him increasingly evil (perhaps with a connection to the original Dark One?). Maybe Henry contains enough goodness in his heart to counter the darkness of all those shadows.
I think this is likely and it plays into the theory many of us have that the result of the encounter with Rumple, PP and Henry will result in Rumple losing his Dark One persona in order to save Herny.
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"He was a lot of things to me" "The only conclusion was love"