I have a dictionary that I keep around specifically because of the definition it contained for a single word. That word was the word ‘belief’. I have seen other dictionaries since that had a similar definition (specific to one word in particular included in the definition) but essentially it described it as “something considered to be true or factual without proof“
The important part being the concept of proof or the lack thereof when describing a ‘belief’. I used the term ‘belief’ systems in the subject because I’m not just talking about religions. (although they are one of the more notorious beliefs espousing altruism as a goal or as part of their core philosophy) Marxism and environmentalism come to mind when speaking of other belief based movements that require some level of selflessness and individual sacrifice to a higher ideal.
So where does the hypocrisy come in? Well all of these things require some level of ‘belief’ in their primary premise (the existence of a higher ideal or purpose than one’s own self-interest) prior to following the doctrines associated with that belief. Although there is generally some attempt to or existence of pressures from the other ‘believers’ to encourage the ‘believing’, ultimately the nature of belief (without objective proof) comes down to a choice. So essentially a belief is little more than an ‘opinion’ (albeit a shared one) since it involves a personal choice by each individual follower of the belief.
Well if that belief (opinion) asks one to be selfless, what possibly can be more selfish than holding an opinion?