I don't think Detective Miller knows how to turn off his instincts. He executed the boss as soon as he got a conformation there were others, who could control the system. In his mind, I believe he were righteous and what he is doing in the memory of Julie, is all sanctified.
In his mind, humanity didn't need to learn more about the protomolecule than what the dead boffin revealed. If he hadn't done that, they wouldn't have learned about things about the feed as they've done now.
A lot of his actions are unexplainable without the narrative. And so far they've been mixing in bits from book 3 and 4 as well. As always I don't want to spoil anyone with my advanced knowledge, because what we see in the small screen is different to the books, and some things that were covered with a para get minutes of screen time.
I'm not really sure where they are heading, so even though I know, I still know next to nothing about the Expanse.
Detective Miller cannot turn off the detective part. It's part of him even if he doesn't have that bloody hat. That's all I can say.