: If Galadriel had given Feanor a lock of her hair when he begged her, would this have satisfied his desire for the Light of the Two Trees, therefore he wouldn't have made the Silmarils, which would have prevented the Revolt of the Noldor, the Ruin of Beleriand and the events leading up to the War of the Ruin etc.

No. Galadriel made a choice. She is in no way responsible for Feanor's response to that choice. Blaming all those consequences on Galadriel is on the order of a ki saying "look what you made me do." Nope. Feanor is a being with free will, like all of us, responsible for his actions.

As a "what if," though this is interesting, but Melkor was still on the loose, and very good at doing what he does.

My interest, when reading this passage (in _Unfinished Tales_) was the light it shed on Gimli's gift. What a contrast: Feanor is making a demand, based on pride (mixed, perhaps with unadmitted lust, or envy or both); while Gimli makes his request in a spirit of humility.) Galadriel has had 7000 years to grow out of any pride (or hidden pleasure/spite at thwarting her cousin/half-uncle or whatever the relationship was). Gimli's request does not elicit the memory of Feanor, for Galadriel at least: can't speak for Celeborn, who would only known of that story second hand.