Tahiri
Perhaps it isn't so much going backwards, but taking what you have right now and working from that. Because in essence, all of those are you, and we are but a sum of the parts we were before. I still have the Emperor's Hand in me even now, for example. That question may be better suited for Luke, but I think some of them can be used for good if used within the right context. But there are abilities that should not be used because they come from the darker, more dangerous side.
I know my opinion on some of the abilities could be surprising, but let us say that he used an ability to save my life here when I'd contracted coomb spores again. So I cannot completely condemn such things when used in the correct situation.