DFC. You may be mis-interpreting my original point.
I would never condone the switching off of useful safety nets. They are there for a reason. TCAS, like STCA, is a valuable aid and should be used if it's available, but we must remember it's lititations.
In some instances, however, it may not be practical to use all available aids. If I am working a high performance aircraft doing aerobatics between ground - 5000', then that will be the only local aircraft in the area. Other aircraft may be held at visual reporting points or routed around. I will have informed the relevent adjoining sectors and any airspace required will have been co-ordinated.
Under the circumstances described above, I will not require or desire mode C info from the performing aircraft. TCAS, great as it is, does not universally respect airspace boundaries. TCAS is designed to provide emergency traffic info & separation of IFR aircraft in situations where the system has failed and radar separation is lost. Pilots are briefed to obey TCAS RAs over controller instructions, so if an RA is triggered, it will most likely be obeyed. This could potentially have disastrous results if it is triggered as a result of an aerobatic climb. The aerobatic aircraft will most likely be okay, once they reach the top of climb they usually go back down again. But the IFR cruising aircraft that responds to the RA will go where...
... and hit what ... STCA prediction alerts that are triggered as a result of (rate of) aerobatic climb (loops etc) are a distraction, and can also be potentially dangerous.
I condone the turning off of mode C for aerobatics, ONLY in controlled airspace where alternative and sufficient precautions have been taken. The reason for this is so as NOT to trigger spurious STCA alerts or TCAS RAs.
If operating outside of controlled airspace, continue to use mode C.