My reasons for not drinking are:
1) I have seen the effects of alcohol abuse close up in my extended family and have no desire to take any risks with it. No one sets out planning to become an alcoholic.
2) People often use alcohol as a way to either spend time with people whom they have nothing in common with, or as a way to feel comfortable enough to interact socially. With the first, they need to find other company and with the second, alcohol is actually preventing them from growing as a person.
3) Where I live, I have seen alcohol serve as a distraction from dealing with problems that need to be resolved at home. This usually results in bad behaviour and in people banding together to justify the time spent away from their partner. This has been the demise of many relationships. In addition, with company, it is easier for someone to be in self-denial when they are developing a drinking problem.
4) It impairs judgement and I don't like not being in charge of all my faculties. I also would like for people to be able to respect me and for me to respect them. This is harder when one or both are not working with all of the decision making abilities they normally possess.
5) It creates divisions between people. Those who don't drink are often seen as judgemental or are left out socially. Those who do not know how to drink judiciously also suffer negative social effects.
6) Drunk people are unpredictable. Other's safety and welfare is often compromised whether through drunk driving, neglect, fighting, or (inappropriate) sexual activity.
7) The health implications of drinking are still undetermined, but it appears that there are more negatives than positives.
8) Even if I can handle it well, there are many people who cannot. Every person who participates puts on pressure (knowingly or unintentional) for others to join as well. By hosting a social gathering with alcohol, I am making those conspicuous who do not join in. There are those who are underage, or who have had a problem with it in the past whom I don't want to put in that position. It also says to the younger generation that serving alcohol is part of being a good host.
9) The capacity for thinking of the effects of their actions on others is diminished. This leads to noise complaints, hosts having to ask certain people to leave, fights breaking out, gossip being spread, inappropriate flirting and so on.
10) Partying is an expensive habit.
I am aware that many people do drink in moderation. For some that works well. For me, I think it softens up the line in the choices I have made. At what point do the aforementioned points go from being invalid to coming into effect?
I myself do choose to spend time around people who drink, but leave before people are drunk. I don't go out to the bar, as it seems odd for me to go somewhere where I am not going to take part in the main activity, I don't like the unpredictability of drunk strangers, and I don't like being on the road with other patrons who have been drinking, even if I am the designated driver for my group of people.
I don't look down on those who choose to drink socially if they are responsible, but would never choose a partner who does (I have dated someone who did drink socially and it became a point of tension in how we hosted social gatherings, behaviour when we were out, who we spent time with, choice of friends etc.). If we were to have kids, I would want to be giving a consistent message to them about alcohol.