I very much dislike the second sentence in this tag: "If you do something to feel good about helping people, or even to be a better person in some spiritual sense, it isn't truly altruism."
First of all, it's cryptonormative. Second, it leads to the old "people only care about their happiness" model that explains everything. Third (but this is a weak & contextualizing point), it is related to the common perception that egoistic actions are usually bad.
I have replaced the second sentence with "However, non-altruistically motivated actions can still be good (e.g. people pursuing non-rival goods), and altruistically motivated actions can still be bad (e.g. people being mistaken about what is good).", and added that altruism is a motivation rather than a set of actions, but this is rather preliminary. I would be equally fine with the second sentence being deleted altogether.
I have removed the good/bad duality entirely, as I found it confusing.