Excuse me. You would ignore an RA?

Absolutely wrong. If you have to other traffic visually while you follow the RA great. But you always follow the RA (Exceptions: Terrain/stall warning)

The crew in question would have had a midair collision, had they followed the TCAS.

Please don't get me wrong, I've always followed TCAS RA's, but not blindly so. Doing so would be akin to blindly following a FD.

But in IMC, or at night, or if the TCAS traffic is directly above, below, or behind you - i.e. you can't see it - you still must follow an RA, no? (unless GPWS etc).

Even if you think you CAN see the traffic; that might not be the aircraft the TCAS is avoiding.

Bit like PWS detecting windshear that you can't see.