Haste has pretty much covered it.
An example: as an Outcast, you see a GRN in Tau-23, who is your enemy? Why do I have to RP before I shoot him, enemies wouldn't talk!
You do it because the rules say so, and they do for bases as well now. For a player, whether they are a snub or a silent trader, just because they don't reply doesn't mean you can't shoot them. Just "drop your engagement notice" before shooting, same as you do for shooting player ships.
There might be a slight tweak on the wording of that rule, there might not.