We have to remember that at the time of the decision, there really wasn't any source of things to copy with a Betamax recording device besides commercial broadcast TV and other copyrighted materials.

Camcorders and such devices where you could make your own content were very rare, if available at all.

This speaks to first principles. I don't want judges making law - and any good judge doesn't want to make law. Laws are from elected legislatures. Of course this is all wishful thinking.