On the other hand, if Staten Island were willing to secede on even terms we should let them. They'd be worse off, marginally, and we'd be better off, marginally
No both would be worse off.
Staten Island would be worse off because property taxes would have to go up significantly.
NYC would be worse off because the loss of Staten Island would lower the City's share to about 38% of the state population, tipping the balance of power. Don't think the City didn't know this when they opposed secession.
This last would be exacerbated if Staten Island secession encouraged Eastern Queens to secede as well.
But, hey, who said freedom was free?