The dark side is taint and by running it through the sabers it arguably gives them a lot of power but is also killing them.
I remember George once saying that the Dark Side is a corruption of the Force and not the other side of a coin. I think he changed his mind that at some point, and parts of the Clone Wars made it seem like the Dark Side was in fact just the other side of the same coin.
But the idea that the Dark Side is killing the crystals sorta reinforces the Dark Side = Wrong thing.

