I don't think the decision not to defend/evacuate Coventry is the chief of the criticisms against Churchill. I don't have any problem understanding why he allowed it to be bombed. But I also think there are lots of legitimate criticisms of his arrogance and, at times, bloodthirstiness. Dresden is top of my list.
I don't buy this moral distance argument though. There are plenty of things going on right at this moment that I have absolute no problem condemning. I don't need 80 years of hindsight to see they were wrong. This isn't superior morality, just, most of the time, common sense. The idea that we're helpless moral beings in real time doesn't really make sense.