Basically I wholeheartedly disagree with your therapist. I've not had any 'clinical' mental problems as such, but I've been pretty screwed up from time to time, and the thing that got me through it was focussing on other people's problems, offering counsel etc, mostly to distract myself from my own problems, but in doing so I gained an insight into my own situation. In helping them, I helped myself.
So yes, do offer them advice, but be prepared for it to be resisted, or even outright rejected, especially if your friends' problems stem from emotion (eg. relationship issues, addictions, etc) instead of faulty logic. Even though they are your friends, they can still get offended by what you say (naturally, if their current thought process is being challenged, the first thing they'll do is go on the defensive.)
Also remember, that by judging other people by your own standards, you are harming the relationship, rather than helping it. For example, by reading your posts it is clear to see you are not at all keen on alcohol. This is fair enough, and it is true what you say that logically speaking, consuming vast quantities of alcohol to the point of nausea is abhorrent. However, humans are rarely logical creatures, and everyone has their own weaknesses. In this situation both parties have to work together to come to some sort of compromise that will be beneficial to both parties
For example, let's say one of your friends constantly gets drunk and acts like a douchebag whenever you go to hang out. Telling him/her to stop drinking completely will be pointless at best. If you could persuade him/her to drink less or get drunk less often, then you both have a partial win. He still gets to drink, and you get the satisfaction of knowing you've helped him while keeping the friendship intact.
I've gone completely off on a tangent so I'll stop now. I hope this helps.