I've been pulled over dozens of times, and there's always questions asked.
Never pulled over for impeding traffic though. I'd make it my aim to pull over an equal amount of "idiots" (slow drivers) as "maniacs" (fast drivers) if I were a police officer though. Most states require slower drivers to pull over to allow others to pass, but hardly anyone does that. I'd certainly be throwing the book at those "idiots".
If people aren't comfortable driving at the pace of at least the slowest traffic and impeded the smooth flow, they've got to go. Plenty of other ways to travel for those wanting to go slow, like take a bus.
Very unprofessional of the officer to not discuss the situation though. If there was behavior that needs to be corrected, that requires a dialogue. Every time I've received a "warning", the officer at least said something like "slow it down".