system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] What is it about the dark side makes it so damn hard to leave it?

I'm currently, as I type this, watching the 6th Star Wars, 3rd one released in the original series.

I just got to the part where Luke turns himself in on Endor and asks Vader to come back to the light side and he says he can't.
Why? What's so appealing about the dark side that he completely shut out family and love for his son and is willing to murder his own son to obey a master such as the Emperor?

Is the dark side like a drug or state of depression that clouds everything you know and love? 

I love Star Wars, that's just one of the few things I never understood. Why does Vader feel like he HAS to stay with the dark side.

EDIT: Vader just said "It is pointless to resist [the dark side from the emperor] my son."
Does this mean Vader knows the dark side is bad but can't resist? If so, why?
gpt
To understand why the Dark side is so irresistible you have to know what the Jedi go through in training and what they're taught. They're told from a young age to suppress certain emotions and that ruling people is not the Jedi way.

Let's say you're a 14 year old impressionable Padawan. A strange man approaches you and tells you that all of those feelings of anger and lust you've held at bay are things that can actually make you a better, stronger Force user, wield a lightsaber better and create peace instead of sitting back and not interfering.

Of course there is more to the Dark side of the Force than just letting in certain feelings, but that is the start of it, and once you begin to delve into it, do you really want to go back to suppressing yourself again?

Vader is given the choice by Sidious to become more powerful as his Sith apprentice, to save his wife and children, or to be a good Jedi and potentially let his family die. Unfortunately for Vader there are some things that you just can't go back from. By the time Return of the Jedi rolls around, he has murdered countless people across the galaxy to better the Empire, including the slaughter of the children at the Jedi temple.

For Vader it's not a case of being able to resist anymore, it's trying to live with what he has become. Of course he knows that the Sith and Dark side are bad, but he's destroyed the only family he's really had, where else can he go?