All of these reasons to help others seem fine to me. Other people are in worse pain, so give them some help. If it makes you feel valuable, that your life is worthwhile, that's nice, you're going to feel good about yourself. When you make other people happy it makes you happy - that's fine. When you don't help others you feel guilty - that's another good reason to always help others. Those are all good reasons as far as I can see.
I guess the main question here comes at the end, "Sometimes helping others seems like an addiction causing harm to myself, how can I stop asking too much of myself?" OK, we do have to be careful in balancing what we give others and what we give to ourselves. Anyone who's been in a helping profession, doctors, nurses, social workers, meditation teachers, anyone in a helping profession has to watch out for something called "burn out". It's very common. We give, we give, we give, we give - we get so caught up in the giving that we get exhausted.
Having an addiction of wanting to help others can also be tied in with avoiding doing any work on ourselves. Some people actually don't want to do any work on themselves, so helping others becomes an excuse not to do their own work. We want to be careful of that, because we won't last in the long term, we will burn out and be left with nothing. So we need to take breaks and alternate between giving a certain amount of time to others and giving a certain amount of time to recharging ourselves.
We've had many students who are social workers, psychiatrists, doctors and nurses. They know the importance of coming to the retreat, they know they need to recharge so they can go back and give more to others. That's where you find the balance, you've got to make sure that you give to yourself enough. Now, how much is enough? No-one can put a figure on it, you've got to see for yourself. But if you are getting burnt out, then you haven't had enough rest.