Straw man. There's no reason these exploits couldn't have been executed in a parking lot (where, in fact, the rest of the test was performed). They would hold the same impact without endangering the public.
This is the same reasons that dangerous medical research is performed in negative room pressure clean-rooms and vehicle safety crash tests are performed in controlled environments and not with vehicles on the interstate. You don't expose uninformed, uninvolved, and non-consenting members of the public when performing dangerous work.
As it was, he stalled out on a bridge in heavy traffic and managed to get to safety. It's not much of a stretch to imagine a worse scenario - there he is in a tight turn in heavy traffic when his vehicle is compromised. Imagine he hits a minivan with 5 kids that then rolls. Now it's not a story of a dedicated journalist and two edgy security researchers - it's a story of murder, or at least manslaughter, and all three are complicit.