The simple fact is, if both had Mode C and even one had TCAS, the accident would have been avoided if the RA was followed.
Mode C was compulsory in the USA more than 25 years ago, it is mandatory in Belgium airspace. It's should be mandatory in UK.
For those dinosaurs anti-TCAS, turn yours off if you have one, but keep your Mode C on. Then if you're coming up behind me fast I do not die if your lookout skills are lacking. I don't want to die due to someone's poor lookout so I will keep my TCAS on. (there are enough studies to show that lookout for collision avoidance is a flawed policy)
But remember if that jet at 250 kts coming up behind you doesn't see you and is also anti TCAS (and has it switched off to improve his lookout !!) .. you may wish you had TCAS in your final moments.
Yesterday the weather was good, what if the visibility is 1000m and two aircraft are on a collision course at high speed. Mr lookout may not have a chance to avoid. What if IMC?
It's time to do something to stop any more unnecessary deaths. Mode C allows ATC to provide a safer "traffic service" and allows RA's to work.