"The tiny number of lives lost to this type of accident will never justify this proposal."
I agree.
But that's not the same thing as saying (as others do) that looking out is THE solution
A very big distinction.
"It would, after all, ground about 70% of the traffic"
Do you have a reference for this figure?
It's going to happen anyway, a few years from now, but at a more expensive point because a Mode S unit currently can't be put in for under £2500+VAT.
If Mode C had been made mandatory say 10 years ago, every plane would have one (they start at about £1500, about the same as a radio+VOR) and there would be no fuss about it now.
Then, instead of an RIS traffic report
"traffic at 10 o'clock, level unknown"
(almost useless, like the majority of them) one would get
"traffic at 10 o'clock, same level"