Wow. I got your blood pressure up, I guess. I'm going to have to disagree with you a bit.
It is the Captain who has the sole responsibility for the aircraft, crew, passengers and cargo. Busting mins or flying into a level 5 is a different matter, and it is indeed the FO's responsibilty to ensure these things do not happen. Operating a legal and airworthy aircraft that may or may not be too hot is more subjective, and the capain is the one charged with determining this. The FO can, and in my case is expected to offer his opinion as part of the crew, but I assure you he/she will not be getting the phone call from the director of ops or chief pilot to explain it. If you want to make your own decision because you disagree and walk off the flight then have at it. You will do your own explaining. AM I saying FO's should shut up and keep their opinions to themselves? No, absolutely not. But I stand by my original statement that it is not your decision, because it is not. My FO told me last week how I needed to or had to tell flight control we would refuse the a/c after a roundtrip without an APU. But, guess what, clouds rolled into ATL and the outside temps cooled to about 25C. We parked at a jetbridge with ac, and I figured we were going off the north side and it would be a short taxi. Taking his opinion into consideration (and the FA) I decided to continue with the plane to try to keep some sort of scheduling integrity. Maybe you would have done different. But, the parameters set in our FOM were not met, Flight Control said it would take a long while to get a change in a/c, and that was my decision. It was not a democracy....but you keep on thinking that it is.