Bingowings said:

From Anakin Vader's point of view the Jedi and Obi-Wan have been revealed to be just as corrupt and dangerous as they taught him the Sith were so I have no problem with him using a blade given to him by his new boss.

It also keeps the blade Luke gets from Ben 'clean'.

By having Vader reject his Jedi weapon and take up the colours of a Sith Lord it leaves Ben free to pass on the baton of Jedi Knighthood to Luke and not that of a wife strangling, infanticidal egomaniac.

Yeah, but you can also argue that it adds even more so to the reveal that Vader is Luke's father. Luke's been following in the footsteps, and using the same blade as one of the galaxy's most notorious mass murderers. It adds to the mind **** of the whole "I am your father" thing.

And just the idea that Palaptine would feel that Vader ABSOLUTELY NEEDS to use a sith weapon when he already has a lightsaber of his own, is just kind of weird to me. But I dunno, that's just my opinion.