Especially when said monopolies actively manipulate consumer's perceptions of what a fair price is to begin with.
Witness the premium Intel put on 4+ core CPUs for ages, then suddenly when AMD picked up pace, they could deliver them at half or a third of the price...
Witness the premium Intel put on 4+ core CPUs for ages, then suddenly when AMD picked up pace, they could deliver them at half or a third of the price...