Good topic - I enjoy philosophizing about bodybuilding.
First, since you seem to be asking for clarification on terms which have no doubt emerged in conversation with a 'natural' bodybuilder, I must say that there is absolutely nothing 'natural' about bodybuilding - drug free or juiced to the gills. Natural in its most strict definition (as an adjective) would be 'arising from nature' or 'uncultivated.' As a noun, natural would be 'any person or thing that is or is likely or certain to be very suitable to and successful in an endeavor without much training or difficulty' - as so eloquently defined by dictionary.com. Thus, we see that the bodybuilding lifestyle is inherently UNnatural - it is totally cultivated, planned and extremely difficult! (For 99% of us that is!) I don't think anyone, including your friend, is going to try to argue that point.
The REAL issue at hand is drugs - which is a moral debate, one that you will never win. If religion is a way of life governed by belief, then bodybuilding definitely has religious undertones...and let me say: you'll never make a Jew out of a Muslim! Just food for thought.
Now for my definitions:
1. Bodybuilding: the process of transforming one's physique into his or her's ideal self-image - literally building the body into a piece of living artwork.
2. Progression: the act of moving closer to a goal.
I suspect that your conversation may have led to someone saying something to the tune of "performance enhancing drugs are the means by which progression occurs after a certain genetic limit is achieved." ...And this is where the can of beans gets spilled all over the floor and we get to delve into much deeper things like norms, morals, health, right, and wrong, etc., and the whole 'religious' aspect emerges. The clash between 'natural bodybuilding' and 'bodybuilding' is nothing more than the old "I don't like the way you belive" debate that people have been killing each other over for literally thousands of years...it's just toned down a bit because we all know that it's less important how big and strong one's muscles are if he or she worships the correct deity. More food for thought.