I was grateful for a neighbor's unsecured wifi during a big hurricane scare a few years ago. We evacuated 200 miles (in 19 hours) to my grandmother's then empty house. The power was on, but her phone was off and the TV was gone, as she had moved to a retirement apartment. We desperately needed weather information to know if the hurricane was still headed to our homes (fortunately for us it turned). Someone's WiFi saved us through the next half day. I would have gladly told them thanks if I knew where they were.
This doesn't directly address the ethics question, except to say in some situations it's like speeding to the hospital with your wife about to deliver. You make exceptions, and would be glad to continue the kindness to someone else in the future.