This is definitely me when I'm not parroting state propaganda!
This is part 1 of our new Libs of Lemmy series. If you wish to contribute, just make sure you include Libs of Lemmy in the title. An award* will be presented for capturing the biggest lemmy lib, so get posting!
NSFW spoiler
*one-way ticket to official CCP cbt + milking dungeon
I think it's a combination of thought terminating cliche and in-group signifier.
"You're a bot/Russian agent" completely dismisses everything you have said and could possibly said and shuts down the conversation. It's a textbook thought terminating cliche. They can throw your entire argument out while protecting themselves from cognitive dissonance.
And then it also signals to their fellow libs that they can disengage, the enemy has been discovered and dealt with, we have won, blah blah blah. If anyone questions it or continues engaging they're undertaking a very small risk of being challenged by their fellow libs ie "why are you arguing with them, it's just a bot, come back to our safe lib spaces where we will talk about the GDP and nato's new cluster bomb that mulches 3% less infants".