Every selection is arbitrary in what sense?
[WS:] In the sense that the perceiving subjects have a choice between different alternatives, as opposed to being compelled one of these alternatives on the pain of being at odds with the facts. Of course, individual choices may be also constrained by collective norms, but that does not mean that collective norms are not arbitrary in the sense I just mentioned - that they are not contradicted by objective facts.
To apply this to our discussion of the media - media outlets are arbitrary because they choose to report different facts based on their political or cultural preferences, rather than because something objectively happened or did not happen in a particular way. Their reporting reflects two things: what actually happened (which can be objectively verified or falsified) and how this fits into their larger outlook or "weltanschauung."
Now if you want to debate the virtues of science, "objectivism" "essentialism" and the assorted word salad that pomo logorrhea managed to produce, I suggest proceeding as follows: let's start with walking up to the tenth floor of an apartment building, jumping from a window, and then discussing the objectivity of the laws of applicable science (thermodynamics in this case.) Since it is you who seem to doubt that objectivity, may I suggest that you volunteer to perform the jumping part? It should not matter if it's all arbitrary and subjective, no?
Wojtek