There is no theft of service until you take a train to another station, and then jump the gates there to exit.

If you want to get around the gates to enter a station without a ticket, you can just ask the staff. I've done it a couple of times in Japan. You can get inside to look for a lost item or whatever. They even let people in to access the station shops. I watched one tourist ask for that and be granted.

Also, one time I entered a station without swiping my Suica card through the machine. I explained that at the destination station and where I had boarded; they cheerfully fixed it up and let me exit. There is room for mistakes without being automatically branded a thief just for being there.