Hai, it is stealing. But they aren't a bad person. Sometimes you can do things that are wrong, but it doesn't make you a bad person. I know Agito isn't a bad person, and he's done lots of bad things. But he was doing it to keep me safe.
You're only bad if you mean to do the bad things...and you don't regret it or try to do something to help afterwards. Sentience-san only looked at the law side of things. But sometimes it's not always right...
[Having strong views on this is weird to him...he's normally not so insistent. But then again, this does kind of involve Agito and Kaito, so...]