With Full Self-Driving available on demand, be wary of any and all Teslas

In the past week, Tesla's Full Self-Driving beta program went from about 2,000 select drivers testing it to almost any Tesla owner in the U.S. willing to cough up at least $200. U.S. drivers make up at least half of the more than 1.4 million Teslas worldwide, so there's a lot more opportunity to encounter someone with the hands-free, not-quite-autonomous driving mode engaged. Other drivers likely won't know when a nearby Tesla has FSD is turned on, but if they see one struggling on busy city roa...