How about I don't want my friend to drink?
There's nothing wrong with a little bit of alcohol. Why do you want your friends to avoid drinking alcohol?
Because drunks are losers
It's totally okay to worry about your friends unhealthy habits.  However, worrying should be the extent of what you do.  You can't tell other adults how to live their lives.
I get so stress about it but I guess it's fine.
If he is just drinking in moderation, maybe you are over thinking it. Some alcohol, like a bit of wine, is actually good for you. As long as he is not a drunkard, maybe you should just let him drink and don't try to stop your friend, or there will be unnecessary tension in the friendship.