I tried alcohol quite young, only the odd taste - and I hated it. I grew up and kept the hate of it - before I went to University I was straight out "I'm not going to touch a drop of alcohol" - first night there, I had a few Vodkas and Coke. I started drinking - it was hard not to, one of the most integral parts of student culture and life is that you drink, and you drink lots. If you don't, you find yourself outside alone a lot.
I got drunk one night after a five hour train journey from home, I hadn't eaten and I was tired - the people on the bottom floor of the halls were playing some drinking game and I just sorta joined it. 14 shots later I was a little worse for wear. A few more shots and I was having trouble sitting down. On the floor. Against a wall. Eventually threw it all up, felt like I was going to die, world spun and for two days I was hungover and sick as heck.
After that I didn't want to go near a drop of alcohol. Since then, I've drunk twice. And both of those have been stupid mistakes.
I remembered why I don't like to drink. It ruins people's lives. It's harmful to your health. It reduces your judgement. It makes you do stupid things, such as cheat, fight and just generally be an idiot. It's popular (I know that's a very cliche argument for why not to like it, but I often don't like to follow a crowd, I prefer to do things my own way instead of what everyone else is doing). It's expensive. It's a bad thing to get sucked into. It's also a bad encouragement for younger generations.
I could find no reason, and can find no reason to drink. If people need to drink to relax, then fine, that's their own problem. I can see why a lot of people do though - it's not nice to be excluded because you have better judgement. I think it's as bad as, if not in many cases, worse than smoking.