Buoyant1:Personally, I don't see my certification being a "license" to Dive...If I want to do that I'll just take a resort course, pay a little extra and take a little time extra each time, and do my dives with a certified pro... I see getting my certification card as a means to KNOW what the heck I'm doing in order to keep myself (and others) safe.
The COURSE gives you that. The card is a credential. The credential represents to OTHERS that a (supposedly) trusted third party that you (supposedly) know what you're doing.
The four years in med school make sure you know how to cure people - the sheepskin is just a representation from a trusted party that you have in fact demonstrated that you know.