Unfortunately, Robert Cobb didn't have an AR-15 (or Glock, or etc.) to discourage the thugs. His beating was part of the context for R having his AR-15.
From the little I've read, WI's gun laws are a bit convoluted due to historical evolution and accommodating hunting and such. Proggies, of course, do not care that R was actually in compliance with WI law, and neither, obviously, do Binger & Kraus.