but he had been pulled over by cops 52 times with a total of 86 charges

"Less than half of the charges were ever prosecuted, with Castile pleading guilty to minor counts that included driving with a revoked license and driving without proof of insurance."
"The charges most often dismissed were failure to wear a seat belt — along with driving without proof of insurance and driving with a revoked license."

Not exactly violent criminal status at all. I highly doubt the cop knew this guy because he got a lot of seat belt tickets. And even if he did know of him, so what?

He told the officer he had a gun, and then he reached to a place the officer could not see.

Yeah...and? Are violent criminals in the business of informing cops they have guns? Also, "Castile also announced that he was reaching for his wallet before Yanez, on the job five years, started blasting away, according to Reynolds."

I don't see any "devil's advocate" here because there isn't anything wrong with what the Victim did. It looks more like victim blaming.

police hear stories of their fellow officers being shot and killed.

Then quit the job if your fears are preventing you from doing the job correctly. No one is forcing you to be a cop.