using a neighbors wifi: is it stealing?

[Banquo's Ghost]

Assuming the owner of the wifi router has unlimited, unmetered internet access, using the connection without permission would be more akin to trespassing. Nothing is being taken, but someone is on your "property" without your permission.

That's a big assumption. Here, many people have cheaper deals for broadband based on capped limits. Even so-called "unlimited" bandwidth is nothing of the sort, subject to a "fair use" cap. If one exceeds the usage cap, one gets an extra charge.

So a piggybacker may well cost someone real money by exceeding the owner's bandwidth. Still not stealing?

This is where, I think, arguments for "no injury, no crime" fall down. They assume bandwidth is an infinite resource. I would not be happy if someone linked their home up to my electricity supply, and nor would I be keen on freeloaders on my bandwidth. I would consider both thieves, however sophistic their excuses.