As much as you love ALL of your friends, it is very important to have (and cherish) your completely sober friends. That is, if you are choosing to live an alcohol-free life.
1) Even if your drinking friends only drink on occasion or never drink too much when they do drink - they still drink. When it comes right down to it, they still see alcohol as an enhancement to an evening or to an experience, and buy into the story that alcohol is good in some way. If you don't drink you will have analysed this concept (a lot) and come to the conclusion that, like cigarettes, crack or junk food, moderation is not okay. You don't need to bring this up, or not spend time with your friends because of this difference, but it causes a degree of separation between you - one that doesn't exist with a friend who is like-minded and is on board with your understanding of alcohol.
2) Friends that drink keep a different schedule than friends that don't. Not to say that people who drink don't get up in the morning and exercise, work and enjoy their lives, but when they relax and spend time with friends, there is again, a focus on alcohol as a key priority for having a good time. This can lead to changes in mood, personality and availability. Drinking typically happens at night. It causes sleep deprivation and a deterioration of health. A friend that drinks is less likely to meet you in the morning for a workout or a yoga class or healthy shake - and if they do they will be feeling some level of withdrawal, lack of sleep or a hangover of some kind. They will simply be less available for genuine, positive, giving interaction. Alcohol is a drug, and causes changes we cannot deny. Not to say people who are alcohol-free are the most positive people, but they aren't working with the physiological and psychological challenges a drinking person faces when recovering from drinking.
3) People who don't drink support others who don't drink, and are relieved to spend time among other sober people. We know what it is like to go to a party where others are drinking, and experience the discomfort that comes with this social scenario. People who are drinking want to be certain you aren't judging them for drinking. They also want to be sure they aren't making you uncomfortable by drinking around you. They might be of the mindset that says - since you don't drink, you must have a problem - like, you might be an alcoholic, so therefore you will be salivating over the drink they are imbibing in front of you, causing you teeter on the edge of relapse. This is of course not true, but a thought that crosses their minds. Your decision not to drink could be for any number of reasons. In some cases this scene is not a big deal, but in other cases your sobriety makes the drinkers you are socializing with, very uncomfortable.
4) I'm one to say the wrong thing, even though I'm totally sober. It's easy to slip up and let words come out that can be interpreted in the wrong way. The frequency and amount of damage done since I quit drinking however, has been significant. Going to an event with drinkers raises the potential for this kind of accident, and lowers the potential for working it out in a rational way - like an apology. Drinking causes the brain to change, and thus behavior to change. Adults act like child-like versions of themselves, or cause confrontations, or get overly sad or silly. This is by no means a friendship-building platform.
5) It takes one to know one. Drinkers tend to hang out in crowds of people who drink the same amounts as them. Non-drinkers tend to do the same thing. Hanging out with someone who sits for hours on end drinking several drinks can get tedious. Non-drinkers might have a two cups of tea or soda, but they won't hang out for hours and keep drinking. Conversation is great, and we can all talk for hours. Personally, as a non-drinker, I would prefer to be moving my body in conversation, eating or driving, or doing something besides taking a drug that actually deteriorates the quality of the conversation. It's also just really nice to know someone gets you. They get you so much that you choose to live a similar lifestyle. I'm sure vegans love to hang out with vegans - they can talk about their culture freely and participate in the culture without justification, just enjoying their choices together!
As someone who drank alcohol for 30 years before quitting, I can say there are some very strong belief systems around culture and the perceived benefits of drinking. I can also say there were a lot of things about non-drinkers that irritated me greatly - mostly because of my own insecurities about drinking. I don't wish anyone who chooses drinking (and is fine with their choices) to even consider going alcohol free - I'm simply saying that is good for those of us who have quit drinking, to keep a variety of friends.
So if you don't already have these sober friends, go out and build a few treasured relationships with people who don't drink and who will support you in your choice to be alcohol free. These friends will have the capacity to understand you in a way your drinking friends never will. You will also have the opportunity to give to them in a genuine and meaningful way. Your connection will be unique and incredibly valuable.
If you would like to talk about this - please feel free to contact me at email@example.com