There is a significant distinction between no encryption and weak encryption: There is absolutely no way for someone to know whether or not an open AP is a public or private network
Right, but that's a problem for someone else, not for you.
No, I treat that as my problem - I have no expectation of someone not treating my network as a public hotspot if I provided no way for them to know it wasn't.
That is a stupid thing to say, and only a stupid person would say it. It's not damage at all. It's equivalent to picking up someone's car and facing it the other way. It's an annoyance, not damage.
If the person who owns the network isn't very technically literate then it's equivalent to damage - they suddenly won't be able to connect to their own network and will have to hire someone to undo the damage and make it work again. You are making the assumption that everyone knows how to diagnose and fix the problem you're creating which is fundamentally untrue - a significant proportion of the population don't know how to do this and will have to pay someone to do it for them.
Now, if you did that to someone who was depending on it for work, it might cause them actual loss, but someone who is using a network for work and doesn't secure it is an asshole.
Someone who uses weak security on their network either has a legitimate reason for doing so, or doesn't understand the problem. Either way, they are not an asshole - the only asshole in this situation is the person who broke into the network and damaged it in the full knowledge that they were committing a crime.