The NJ test used to have the question “The most important knot is the ________?”
That question was from the "ABC" book and exam, co-authored by the USCG Auxiliary and US Power Squadron, and based on NASBLA requirements. Over time, the section on knots was removed to make way for stuff like BUI rules, CO poisoning and other laws.
But for years, that question was still on the exam.
The most important reason for the card is the privilege that can be taken away if you screw up too badly.
Be careful what you ask for. Many states are calling it a "certification" or simply "education requirement." Once you've been "educated," it's a lifetime thing.
I always correct those who call it a "license." That would imply two things; a privilege which can be revoked on any meager excuse, and an on-going source of revenue for the state.
I'd personally rather not go down that path.
As someone pointed at, even if you don't know the rules, there's a benefit to knowing that there are rules and its not just a matter of who gets there first.
Plus, its something that can be taken away to keep people off the water once they have proven their incompetence.
Its not a perfect system, but its better to have an imperfect system than none at all I think.
It does seem a little impractical to give the same test whether you are driving a jetski, or an 80 foot Nordhavn, but its something.
Yes, the benefit is in knowing there
are rules. But see above about the taking away part.
And since it's just a very basic introduction, mostly about the rules, I think it's perfectly appropriate to get everyone to the same starting point, regardless of what vessel they operate.
Again, the fallacy is thinking these classes are intended to teach you to operate a boat. They are not.
Maybe somebody should point out to the States that most boating accidents aren't caused by a lack of rule knowledge, but instead by intentionally not following the rules or the inability to actually operate the boat competently. 
