Try walking into the skool and "borrowing" the use of their equipment using that excuse. That's not the way it works. Expand your logic to include military or municipal hardware. Walk in to their facilities and demand to use the equipment on the basis of being a taxpayer and see where it gets you.
The local high skool has a swimming pool, which I voted to pay for with my property taxes. However, if I want to use the pool, I have to follow the rules, the schedule, and pay admission for its use. I suggest you discuss the issue with someone in the skool administration.
No problem. Of course you'll contribute a part of the money you're saving, by using their system, to the skool computer fund? It does cost the skool money to pay for the hardware, their ISP, maintenance, administration, abuse protection, licenses, security, and insurance. It's not just the bandwidth that you're using.
Oh, that's easy. Just connect to their network and abuse it for a while. They'll probably find you first. If you hang your dish or panel antenna out the window, in plain sight, it will help them find you.
I can guess the answer and it will be "no". The problem is not your use of bandwidth. It's a security issue. They have no control over your machine or your activities. If you get infected with a worm or virus, it will be all over their network. Since you're on the inside of their firewall, there's no protection for their own machines. If the skool is really cheap and puts the administration computers on the same LAN as the open wireless, then they've put those machines at risk. Apparently, the skool does not turn off the wireless at night, so I suspect there's no competent system administration and probably no security. You may be right that there's nobody to ask. Do you want to be responsible or blamed for trashing their system (even if by accident)?