They're definitely some interesting questions. But they're also a lot trickier than your analogy tries to depict (which, as someone who loves analogies, I understand is often the case).
Mob boss says to hitman 1, "I would like to see Mr. Zulu dead."
College kid says to his buddy while out drinking after they both flunked a test, "I would like to see Professor Zulu dead."
Same statement, yet circumstances are different. The mob boss likely has a history of ordering hits, with a record miles long of the ambiguous ways he's done it allowing for a pattern to form in order to assign definitive meaning and intent to it. The hitman, by the notion of such a profession, likely is a person who has been knowingly involved in various crimes and murders and is thus someone with a means of actually carrying such a request out. There are factors at play within the context of such a scenario that would likely allow for an arrest, and a reasonable one at that, if the conversation was heard prior to action being taken.
With the college kids, likely not? Probably little to no criminal history. Little reason to think the first kid believes the second one has the means to fulfill the request and thus is asking it. No pattern of the vague language connecting to future action (i.e. "he needs to go to sleep. Permanently." --> guy is found dead 2 days later). There's no real reason why it should really even be worried about here (now if it grew into a pattern, then that changes the equation).
There's also this strange fine line between vocalizing a desire to see something, or feeling like something should happen, and actually advocating for or inciting the specific bit of criminality. Added to that, as well, is the actual plausibility of ones speech having any kind of legitimately tangible harming impact. Take these past few months, for instance, regarding Donald Trump. Strewn across places on the net, for example Reddit, you will find all sorts of interesting comments of people vocalizing their desire for, or even the belief of a need for, all sorts of mishaps to happen to him; from violent acts of sodomy to death. Yet despite these things, they rarely cross the line of actively attempting to directly and with intent coerce a person to make such acts occur and thus are largely benign forms of political expression. Similarly, online political agitation is, ultimately, one that is extremely unlikely to actually cause any tangible harm, leading to a high burden to cross to try and really stifle it.