Because Robin thought it was a ‘checkmate’ case that blackmail was good and should be legal.
How exactly Robin comes up with his weird ideas is a mystery that scholars have written many dozens of books theorizing about, but we have learned to rule him in as a thinker who comes up with excellent ideas, and engage with them substantively even if they seem obviously wrong (as was true for Zvi in this instance).
I feel like I’m missing context. Why did this community come to care about blackmail laws in the first place?
Because Robin thought it was a ‘checkmate’ case that blackmail was good and should be legal.
How exactly Robin comes up with his weird ideas is a mystery that scholars have written many dozens of books theorizing about, but we have learned to rule him in as a thinker who comes up with excellent ideas, and engage with them substantively even if they seem obviously wrong (as was true for Zvi in this instance).