If I am one with the Force in life,
Shall I not be one likewise in death?
What then is death to a Jedi?
Lo: But the changing of the tide.
Yet if I despise oneness in life,
Shall I then accept it in death?
What then is death to the Sith?
Lo: Annihilation and ruin.
The dark side of the Force is founded on a conception of the self as a thing separate from the Force. To "master" the dark side is to hold oneself above and beyond the very concept of interwoven life.
Adherents to this paradigm (for it need not be a codified philosophy) ultimately view death as a conclusion or termination of the self, rather than a continuation or transformation of the interconnected web of the living.
All beings live on after death in the Force of Others, whether in the cosmic metaphysical form of a so-called Force ghost, or simply in the ripples of our lives' effects on the lives of others, and of all life that follows.
But to the dark side such life, being absent of control, is not life at all.
The pursuit of the dark side is ultimately motivated by a fear of endings. While there may be other enemies of power and those who crave it, none is greater than the inevitability of resolution, and of change.
Thence springs the seemingly relentless search for immortality by any mean necessary which we witness in those Jedi who have fallen from the light.
Yet, in refusing to die, in placing their will above the will of others and even the will of the Force, they subject themselves to a life of misery, surrounded by the Force, yet taking no part in the fruits thereof.
They transmute the energy of life itself into a mere tool or resource, to be manipulated, spent, exchanged, and ruined for personal gain.
But their curse is twofold: Not only do they live a life of internalized self-exile; they also meet death utterly, even intentionally, unprepared.