Hang on. These are highly sophisticated bits of gear. Of course they are going to go on the blink occasionally. And as already stated, TCAS will work even if the other aircraft only has a transponder ie it's TCAS system is U/S. And aircraft are not permitted into most controlled airspace unless their transponder is working. The 3 day MEL has been in place for decades, on all sorts of aircraft systems. If the FAA want to change the rules, fair enough, but it must apply to all operators.