well, i get where ya' coming from OP. only if gai isn't returned to himself will it be selfish tho. if he gets his foot back, his injuries all heal and he can be a ninja again, its fine.
however, if he doesn't, becomes disabled and just has to watch from the sidelines like an old man when he's all about youth and being active, its pretty cruel because he had already resolved to die, and naruto went and made the decision for him to live (and potentially suffer) without his consent. that's pretty selfish because naruto only looked at it from how it'd make him feel and he just didn't want a friend to die, but when that friend wants to die, its way different.