I am commenting on the letter's contents, as opposed to refuting the poster.
No flashers to avoid a detention? Yeah, right. Like the cop couldn't turn on his lights to allay apprehension in the person about to be chatted with. Then tell the citizen it wasn't a detention, he was free to leave, the cop just wanted to ask a few entirely voluntary questions, the lights were on entirely for traffic safety and to allay the citizen's concern about being accosted by a criminal. "Knowing all that, may I ask you some entirely voluntary questions?"
What we have here is a near-confession that the cop is willing to just up and scare people who he cannot possibly reasonably suspect. Remember, if he had enough information to legitimately suspect PVC, the cop could have used the lights. This encounter was either totally a fishing expedition, or the cop actually did in his mind suspect PVC when the cop did not really have anything upon which to base his suspicion.
Now, if fishing, we can conclude the cop is a bit unthinking. First, if he is fishing, he has to know there is a great chance the guy he is about to encounter is just some Joe out for a walk. Second, here is a guy who is a cop, who practices security and thinks about bad guys all day long, and is certainly thinking about a bad guy at the time. And, he doesn't stop to consider his driving and abrupt exit from the car is going to make an everyday Joe apprehensive? Thoughtless cop. Cop more bent on playing cops-and-robbers than consideration for the citizens.
As far as dangerousness of turning on interior lights goes, the cop could just as easily not made the contact at all. Dangerousness solved.
From the cop's driving, and the initial questions, it sounds like he was suspicious of PVC. Leaving the flashers off to avoid the suspect fleeing runs right up against leaving the flashers off to avoid a seizure. Either the cop had enough to reasonably suspect PVC or he didn't; which is it? The letter writer's arguments are internally fighting with each other. Playing around in the "legalities" grass only serves to obscure that while technically legal, this cop had no legitimate reason to suspect PVC. Yet, the indications are that he did suspect PVC. Great to know some police in Chesterfield are willing to act on unjustified suspicions, and willing to make law-abiding citizens apprehensive.
PVC's encounter was unnecessarily apprehension-inducing at inception. Citizens deserve better. There were other options available to the cop.