And let me guess, the cops' job is to protect and serve?
The situation is both more simple and less simple than that.
Journalists and scientists effective top priority is to serve their employers. Sure they want to report the news and shape truth in the same way that cops want to catch real criminals but all of these people are employed by organizations that have other priorities that take precedence.
Authoritarians hate these groups because they're effectively a competing power center. It's as simple as that. You see the same adversarial relationship between secular authoritarians and the clergy in countries with religious populations. It has nothing to do with truth and everything to do with power. Media, religious, and educational institutions power comes from shaping what people believe, truth in your words.
Scientists are a problem to authoritarians simply because they are educated and will likely refute the bs of politicians, let alone authoritarians.
The hubris in the second half of your second sentence is chuckle worthy though.
Someone asked, ~"what is about those two groups that you like?"
I had to think about it for a minute, but the reply was ~"neither group is perfect, but it's their actual job to find and present the truth."
I have no idea why it took me so long to realize that this is why authoritarians hate both groups so much.