Interesting comments. For the record, I don't have an ethics degree
For me, I suppose it depends on what the outlets are there for in the first place. They are in a relatively exposed location adjacent to a public restroom (whose water and power for lighting is freely used, and meant to be, by the public). They are not locked or switched off from some protected location. Therefore, I think one can logically assume that the outlets are for public use as well.
While I agree that it may be the best policy in general, and good PR for EVs in general, to ask before use, it isn't always easy to get the right or authoritative answer. People will tell you no out of risk-aversion, or just to feel powerful, or because they have had a bad day. They often won't let on that they are not the one to make the call.
liveforphysics, you're a generous guy. I'd happily share my wifi but can't here in the US, home of government by and for the content companies. I don't want to get cut off or throttled because one of my beneficiaries decides to do some file-sharing. And I do keep a gas can, but had to ditch the gas after it started smelling up my car