Teaching by instinct is possible but fuzzy in it's efficiency. In nature, the primary means of function is instinct and its often debatable whether adult animals 'teach' juveniles as opposed to show them: that the adults act in accordance with their nature and their offspring follow and copy them. Animals are far more at home with their unconscious drives and have less of a need for civilized life. They have a sense of family and herding that preserves the species and within that will be a pack defense against predators who hunt in packs. Otherwise, adult life and death is one's own responsibility. Primates and certain highly developed species are exceptional, usually because they have a structured language.
In terms of depression and some other mental illnesses, there's a lot of value in support groups, but putting someone in charge who's actively ill is highly risky. With an illness like depression that can be episodic, someone who's experienced depression and currently in good health can be an effective leader for a support group but they would have to withdraw from the role if they relapsed. They have a greater need to focus their energies on getting well again, otherwise by focusing on a leader who's ill, the group will pick up that person's negative energy and feel even worse.
If we think of this in terms of moving energy, rather than using 'professional' language, having a healthy leader means someone is using positive energy to set limits and direction on the negative energy. That way it's used in a positive manner and becomes positive. For very sick people, good and bad energy can become confused or appear identical. Another idea is that by expressing the negative energy in a focused manner, the underlying positive energy is also identified and built on. To lead such a group, you need to have a strong ego to handle the energy, a conscious understanding about the dynamics of the illness and a supervisor to manage your own health as you channel the negative energy. One powerful quality of a healthy leader is a person who understands how the group communicates and gets them to work on a symbolic level. For a group where people are dealing with depression, this could be something like a relaxation session, symbolic identification of the problem, drawing / painting the symbol and then disposing of it. Or telling a personal story and then re-imagining the ending or writing an epilogue.
Support groups focus on a collective problem. If you have no experience or training for managing the particular problem, the group will at best lose faith and at worst become even more sick. To prevent that happening, they may unconsciously attack you. If you manage to convince them that you have the capability and you don't, the negative energy will be dumped into you, the group will become dependent on you and everyone ends in a real mess. The energy expands the ego like a balloon, but without the strength and elasticity that comes through knowledge and training, it pops and spills everywhere. Alternatively, the energy doesn't overload the ego, instead it takes control. It causes a radical change in the leader, who tries to manage the energy by 'acting out'. In acting out, the group appears to recover, but the leader expresses all the bad habits and negativity that everyone else first brought with them.
This applies to groups of all sizes and once the leader is actively channeling everyone's negative energy, the problem becomes infectious. Corruption, bullying, harmful rituals (patterned behaviours) and substance misuse are common indicators of such a problem. The group is no longer a team with a positive focus, it's become a club that protects it's own negativity and acts aggressively toward others. What's needed is a third person perspective that's rather like friendship but has formal boundaries and responsibilities attached, but there will also be a need for direct intervention. An extreme example of this would be that street gangs benefit from the efforts of youth leaders, but there's also a need for law enforcement.
If we go back to the 1:1 rescue analogy, the idea I first mentioned about recovering is that its not enough simply to recover your own immediate health. Its a very commendable human act to go back and rescue others, but you have to get past your happiness, understand your natural limitations and spend time in everyday life before you can help others. The desire to make things better can be detrimental in itself. Some people will struggle more than you did, some will be in a state of panic and some will even pull you back down with them. To be a life-saver, it isn't just a matter of learning to swim, you have to be a strong swimmer. This even extends to emergencies: the fire service might commend you keeping a crowd away from a burning building, but they don't want you running in there with them. If you can't commit to fundamental training and education, your ego isn't disciplined enough to protect you, let alone for you to help. You don't have to be excellent, but you do have to be good enough. This isn't a matter of personal judgement so much as creditable performance. If you've achieved a particular qualification, people who recognise it will have faith in you and respond accordingly. If its left to you and only you, of course you do what you can for both of you to survive, but you look to help as soon as it's possible.
When things do run smoothly, the shared experience of group working is very powerful. The freedom to experience others discussing a shared problem stops one feeling alone and cut off by it, which is a big deal in itself. It also offers education and encouragement, creative thinking and a sense of improvement through regular attendance. These are all ways of expelling negative energy and recovering positive energy. The popular term these days is empowerment. I'm sure people with magical experience can say a lot more on this. I have no doubt there are comparisons, but I haven't had the training or experience to speak with authority.
If you have a group leader who hasn't been ill in the same way the group members have, they need to have enough mileage behind them to work more as a supervisor than a leader, something like a forum moderator, but with legal registration and accountability. For that you need a strong supervisor and a strong group. A group that can operate this way is largely made up of people who're currently healthy and working on safeguarding against relapses. Their higher level of function is that of a charity: positive press, advising professional workers and supporting other groups.
In summary, illness imposes limitations, but ignorance imposes dysfunction. There's a lot to be said for a common cause, but without knowledge there's a lot of risks and without training, you'll take a lot of time for a little progress.
Unless, of course, you're a genius! 
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