I think I'm in the voluntarily camp.
It bothers me that the husband used the find my iphone feature to find his wife's phone. Having been in relationships with controlling men, it comes off as disturbing to me. It sounds like a very controlling move, one he possibly used in the past to keep tabs on her. She may have just decided to leave a bad situation.
At the time I had a significant other who thought it was appropriate to be tracking the gps on my phone, he also had keylogging software installed on my computer, and my phone and the internet modem would be taken with him when I was left at home alone. I wasn't "allowed" to go many places, even to visit my mother at her house. I didn't have a vehicle, but I did fantasize about just driving somewhere and leaving my phone and getting the hell away without telling a soul where I was going. No one on the outside had a clue any of it was going on.
Controlling or worried? My wife has gone out before and sometimes her phone dies or she forgot it, and if it gets real late I begin to worry. I've called her friends or family before just to make sure she was in good hands. Say for instance no one knew where she was, I would probably try to locate her phone if she had it on her and wasn't answering. We have crazy drivers in CA and there are bad accidents daily. I'd hate to think people would think I am controlling for just being worried or concerned for my wife.