But again the real question is why a TV should need users to accept any kind of post-sale agreement at all to be used normally (meaning "as reasonably expected and/or explicitly advertised").

Maybe the simplest solution is to pass a consumer protection law that completely nullifies any such post-sale agreements and makes pre-sale agreements enforceable only if they have massive prominence and standardised warnings on the packaging like the ones we require here in England on tobacco products. Then everyone can just use the regular tech security and privacy laws against any company that is spying on its customers or compromising their home networks without consent - which would probably be any company that operated this kind of scheme at all because I doubt many manufacturers would want to print "WARNING: USING THIS PRODUCT DAMAGES THE SECURITY AND PRIVACY OF YOUR HOME AND DEVICES" in six inch high lettering on their boxes.