While I certainly see a case to be made that spinner Rumple really jumped at the chance to get the power of the dagger, he didn’t want power for power’s sake. That was the entire point of “Desperate Souls”; he wanted the power precisely because he wanted to use the power to save Baelfire. The trouble is, once Rumple got a taste of that power, it started to consume him. This is an illustration of the old adage “absolute power corrupts absolutely.”
Yes this is true. But I think this is where @nevermore point of control often comes into play: it’s not control in the corrupt way, per se, but rather control over his own life and future. As a peasant and incredibly poor Rumple had no control over his life, or even his death. The Duke could send him (and his child) out to die at a moments notice and there was no way to better his life unless he took the power himself. So while I agree that “power for the sake of power” isn’t Rumple’s story, there is a measure of desperate need for control that does run through him and if we really want to get into this, it’s what @ouatrandothoughts said in the fav/least fav thread, it stems from his abandonment.
I guess the other question this comes down to (besides the one you stated about Belle) is: what does Rumple think his life will be like if he gives up that power and control that the dagger give him? It’s like a safety blanket in many ways. That dagger assures him that his life and destiny are his to command, not someone (or fate) else’s. And maybe that’s his true fear (which is a pretty human one if the show would develop it and explore it in a meaningful way) but instead of being able to communicate that to Belle he makes it out that he’s simply hungry for power.
There’s a impotence theme running through this episode–not exactly sexual impotence (though Hades’s frozen heart and the reaction Greg Germann gave on the bike certainly speaks to that) but the inability to have control over anything: Charmings being unable to leave the UW and communicate to their son, Hades’s frozen heart, Rumple’s fear of what the loss of power means; Zelena unable to do magic when she needs.