Or do you have some other explanation as to why TCAS cannot be used for safety mitigation?
I believe that a TCAS can be U/S for 72 hrs (depending on company ops). I wouldn't want that to be my only safety blanket. The point is TCAS is the 'failsafe' when all else fails; the dead mans brake; the other procedures are the system; not the standard.
If you want to use TCAS to mitigate 'one thing' then you can remove ATC and all other processes too as you can use TCAS to mitigate 'everything'.
That doesn't mean it's "safe" or "efficient"...
I'm not sure why the push for TCAS; when a better industry supported standard would be wide spread ADS-B (in-out) and Mode S... You could put a colocated WAMLAT-ADS-B box at "every" RPT aerodrome and still have buckets of money left over from making the whole RPT fleet carry TCAS; and from what we understand you can't 'break' those boxes unless you hit them with an axe.