What were the great mistakes for the right and left?

Was thinking about what were the great mistakes generally by the right and left in the last century or so. What I mean by that, is an issue on which there was a common view, and decades later almost everyone agrees was the wrong approach.

I’ll start with one for each.

For the right, I’ll cite South Africa and apartheid sanctions. Most on the right argued sanctions won’t work, that the ANC should remain suppressed  that any move to democratic rule would end in a bloodbath.  Basically they were wrong. The sanctions did work. South Africa did crumble under international and domestic pressure and Nelson Mandela did not seek vengeance, but peace. Sure South Africa is far from a perfect democracy – but it no longer has second class citizens, barely better than slaves who lack full human rights.

For the left, I’ll cite the peace movement which advocated unilateral disarmament as the solution to the cold war. They marched in every capital in Europe against nuclear weapons, and demanded the arms race stop. They were absolutely wrong. The soviet empire crumbled as it could not match the economies and militaries of the west. If the left had been listened to, the repressive soviet union could well be still enslaving people today.

So they’re my two great mistakes for the right and left. What other ones would you nominate. They should be ones that most fair minded people today would say they were wrong on. Another example would be those who argued for biofuel subsidies, which ended up starving millions as productive land went from food to biofuels.