H PEACOCK, maybe you don't want to follow the RA instructions, but the other guy and his hundred plus pax might...
Oh dear Square Bear, I'm not sure you fully understand how TCAS works. If both aircraft are operating in TA/RA, have a conflict and follow their respective RAs, all should be well. One of the TCASs probably initiated its RA first, telling its pilot where to go and also through mode S telling the other aircraft's TCAS what it's doing. This second aircraft's TCAS now knows what the first aircraft is doing/going to do and issues a suitable RA based on the dynamics of the situation
and what it understands the profile the first aircraft is now following. If the pilot of the first aircraft has decided to ignore his TCAS then the second TCAS won't know until it detects that the dynamics of the situation are deteriorating rather than improving. It may then have to amend its proposed RA. All very uncomfortable and possible too late to avoid a collision.
So, if the first aircraft has a reason that it's not going to be flying any RA (as previously stated, it needs to have a valid reason) by selecting his TCAS to TA-only he tells the second TCAS it can do as it sees fit from the outset to produce a more timely RA. This avoids the crucial delay caused by having to detect that the first aircraft is not following its RA.
The second aircraft operating in TA/RA will always get it's RA from the first aircraft, but it gets significantly more time to produce a better outcome. Ie, you don't need both aircraft to be operating in TA/RA to generate an RA in the second aircraft. It's important that you understand that.
The point I'm trying to make (obviously not clearly enough for some) is that ignoring an RA is significantly more dangerous than that aircraft operating in TA-only. The decision of if/when to go TA-only is complex and I suspect not something many commercial-only operators would have thought about. However, had I not operated TA only in the examples quoted in my earlier thread, then I simply could not have achieved the mission objective!