Hold on a minute, I think I understand why Kylo Ren is flipping his shit over Anakin's lightsaber now (other than the fact that he's a Darth Vader fanboy since that alone wouldn't be reason to lose his shit as much as he does in TFA). Remember how in the KOTOR comics a character (not going to spoil who) becomes evil for a while because they unknowingly use the lightsaber of Exar Kun? Then how in KOTOR 1 they explain that Revan and Malak became evil because they dicked around with the Star Forge? (Also forgive me if I got that KOTOR 1 thing wrong, I haven't finished KOTOR 1 yet, but so far in the game I can only assume that's what happened to Revan and Malak). Then remember that arc of the KOTOR comic where they explain that the Sith had tons of artifacts that nobody should own because it will lead them to the dark side?
I think the reason Kylo want's Anakin's lightsaber is because it's 'posessed' by the dark side and probably amplifies his powers. It actually makes a lot of sense when you think about it (WARNING: SPOILERS FROM THE SCRIPT OF EPISODE 7).
>Anakin used that lightsaber to destroy the Jedi order
>Luke used that lightsaber for a few years and ended up fucking up all the time
>Even after he stopped using it he got really close to turning to the dark side possibly because he had used it for so long
>Sometime after Episode 6 Lando finds Luke's old lightsaber and gives it to him
>By now Luke has made a new lightsaber so he instead gives it to one of his padawans, the son of Han and Leia, Kylo Solo
>Kylo starts getting into the dark side afterwards
>Kills all his fellow padawans and joins the First Order
>Probably steals other Vader shit during this time (his mask, etc)
>Someone in the First Order realizes how dangerous the lightsaber being with Kylo is and steals it and gives it to the Resistance
>Cue TFA where Kylo is trying to get Anakin's lightsaber back from the Resistance
It would fit perfectly with how they're comparing Anakin's lightsaber to Excalibur as if it has some power to it. Might also explain Kylo's character design since they may have had Revan in mind when making him from the very start. Also note the possible Revan connection since they said Kylo think's he's doing the right thing.