I think it's a bad addiction if the person thinks of it as a way to avoid dealing with real problems.

If I have trouble at work, argue with my mom on the phone, and slip on ice on the way back from the train, then go home, curl up with a good book and have a glass of red wine before thinking about what I can do to solve my problems, and wake up the next day resolved to get help with my work problems, apologize to my mom and wear more sensible shoes, does that make me an alcoholic? Of course not!

But what if I go home, drink the whole bottle of wine and come in to work the next day hung over and even less capable of doing my work, and then feel so miserable when I get home that I figure I need to drink more to make myself feel better? Yeah, that's a problem. (unfortunately someone in my immediate family has that problem. )

If you enjoy being submissive, and it helps you feel better about yourself and gives you the strength you need to solve other problems, that's awesome. If you feel like you need to escape into subspace when anything goes wrong and use the endorphin rush to convince yourself that everything's ok, I think that is a kind of an addiction.