Thank you EricR, your last thread helps clarify "egoist" and "egoism" -- as being the way of being which comes out of the internal subjective feeling of a given person.
I don't know what you mean by "the fullness of joy". But whatever it exactly is, the statement seems to indicate that one cannot experience it without other people. I have deep, satisfying, complete feeling experiences on my own all the time so I must differ on this point.
Okay, that is good to know, and reminds me that everyone has individual preferences and experiences, and so I need to be more careful before I assume a given level of social involvement as being best for everyone.