Don't drink, never have, never will if I can help it.
Why? I'm not religious in the slightest. I am, however, a medical student and I've seen, first hand, the damage alcohol does. I've seen the metabolic disorders, I've seen the liver damage, I've seen the heart dilation and the atherosclerotic plaques.
But there are three fundamental reasons why, even if alcohol was perfectly healthy, I wouldn't drink:
1) I want to be in control of my self. Alcohol can take away that control.
2) Alcohol messes with your brain chemistry, even if temporarily. Being a non-theist, I don't believe in the soul, but I do believe in the brain. We are our brain, and our brain chemistry is a component of our brain's functioning, and as a result, our brain chemistry is a part of who we are. Alcohol will, therefore, fundamentally change you who are, even if temporarily. I don't want to do that. I will remain myself, at all times, as much as possible. If I can avoid psychoactive drugs, I will. Of course, if I need to take medication that affects my mind, I will reluctantly agree to it, but if I can avoid ingesting or taking a psychoactive substance, I will avoid taking it. I AM ME. I WILL REMAIN ME. I will not change who I am for the sake of a "good time" or for a "party".
3) It's potentially addictive. I can't get addicted if I don't drink. I have been in stressful situations which would have caused me to turn to drink had I ever started. But, because I never drank, I never turn to alcohol when I am stressed or in despair. You can't get addicted to something you never started, and you can't abuse something you don't drink.