system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Why is the dark side hazardous to the user's health?

What is it in particular that causes one to get side effects such as yellow eyes and scrotum face? Is is through being evil or from using certain Force powers? If a Jedi used Force lightning to start a campfire or sterilize some drinking water, would he suffer ill effects? How does the Force know if you are being naughty or nice and why does it punish you for being evil?
gpt
This is an analogy I've used before, but think of the force as a flame.  There are plenty of applications for fire that are quite safe.  Cooking, heating, illumination.  You can also use fire as a weapon, but it's pretty hard to do it safely.  
The force is like that.  Because it expresses itself in our reality through the living force, it is fundamentally aligned with life. Creating it, protecting it, fostering it.  To turn it against that purpose isn't exactly *evil*, it's simply inclement to life, and that isn't limited to the person you're using it against.  Using the force to harm is like attacking someone with boxing gloves that you've set on fire.  Fearsome? sure. Effective? Yeah.  Harmful to yourself? No doubt.  
The force "punishes" you in the same way you could say a flame would punish you.  Some applications of the force just aren't.. healthy.  
Again, there isn't a reason to think that the dark side of the force is intrinsically evil, in the same way that a predator that kills to survive is evil.  it simply appeals to the kind of mindset that we often perceive as malevolent.  Bending reality to your will. Power at any cost.