Like any other machine, they are not 100% reliable.
I think that is a pointless comment. Pacemakers arent 100% reliable but presumably you would want one - as matter stands transponders are the best mandated technology we have.
We could go on all day about differences in philosophy as to what is acceptable risk, and what is not, in somebody else's chosen field of aviation.
Your argument would be relevant were it not for the fact that your chosen and my chosen field of operation is the same field. If you wish to stay in your own field then I couldnt care less what you do - as it is you dont.
What kills most in the power GA world? CFIT and loss of control in IMC?
Now you have totally lost me. Malaria kills more people in Africa than Billhartzia - I know lets not bother doing any research on preventing people dieing of Billhartzia.
So, where are the real risks? I know what I think.
The risks are very small on that much we agree. The risk of CAT colliding in CAS if they were not fitted with TCAS is very small. However, a very few accidents were enough to persuade the authorities to mandate TCAS.
See and avoid in VMC has a chance - I can accept gliding in VMC without transponders. In IMC see and avoid has no chance.
I think it is totally selfish to be flying in IMC and do absolutely nothing to avoid collision other than keep your fingers crossed. Be in no doubt, if you are gliding in IMC without a transponder that is exactly what you are doing.