Do you really think reading a snippet like that completely out of context should qualify as probable cause?

Yes!

When you read something describing in detail a person's intent to do something very bad, in a place where they write things that they intend to do, and which in the past they have in fact consistently done, you don't attach any significance to that at all?

	▲	rolosa an hour ago \| parent \| next [-]
		How can you prove that it's not just me writing a dark and morbid story?
	▲	jrflowers 7 minutes ago \| parent \| prev [-]
		How does the cop at the traffic stop know that your username is akoboldfrying? Did you tell them? If so, why, at a traffic stop, did you do that? Are you posting threats on hacker news while you are driving? And the cop was close enough to see your username and what you wrote? Is that why you were pulled over?