While someone perched on a wall outside a private home might indeed be suspicious, the real issue at hand is the cost of accessing a wireless network without permission. Unsecured networks are common, especially in large cities, and many of them are made publically available – but some are simply left wide open unintentionally. Years ago, splicing into someones cable to get free television programming was rare and wasn't considered much of an issue. It quickly became such, and today is considered to be a serious crime. It seems that stealing Internet access by leeching off a wireless AP is becoming such too, with more people seeing it as not just a victimless crime.
Is it up to each individual person to secure their wireless networks? Or should people know better, and stay off networks they aren't supposed to be on?