"But in my view it's not reasonable to design unnecessarily expensive and vulnerable bicycles on public roads, and then get narked when the damage is expensive."
There are two points here. First, each of the three things that makes modern car mirrors expensive are safety features. Electrically-adjustable means people do actually adjust them properly. Heated means they continue to work well in weather conditions which would obscure cheap ones. And indicators in mirrors makes them more visible. It's not frippery.
Second, it's not for the victim to justify the cost of their possessions when someone else damages them. As others have said, if a car driver (or jogger, if you prefer) collides with a cyclist, are they entitled to complain that the cyclist should not have been wearing "unnecessarily expensive and vulnerable" Rapha clothing and riding an "unnecessarily expensive and vulnerable" bicycle when they should have been wearing Lidl clothes and riding a BSO bought from Tesco?