I agree with you, I do not think they will close it.  I also agree with you that people should be responsible for themselves and no one should tell them to wear a helmet.  That said, since the Hudson River Park controls the park, they make the rules.  It is actually better this way because, unlike, say, Riverside Park which is administered by the city, you have to wear full pads to skate!  You say that you own the park because 'we' paid for it and then used the analogy of the streets... well guess what, you are required by law to wear a seat belt (even on hot days) when using the streets as they were intended, to drive on.  You can't even turn on red which is absurd.  The thing is, if you don't like the rules, you DO have the power to change them.  Get on the board of the Hudson River Trust.  Or even better, get the Hudson River Act repealed, making it a city run park, and then get the skateboard park rule that says all skateboard parks with ramps over X height require a helmet.  Today at the park they didn't even send a park employee, the cops came instead.  Is it 'right'? Not in my book, but I don't make the rules and neither do any of us, that is until more places become like Portland and elect a skateboarder to city council.