Whole economies have been ruined by expelling productive minorities who happened to have a different religion or belonged to a different race. After Spain expelled the Moorish Christians in the 16th century, one of the religious leaders who had advocated their expulsion asked: "Who will make our shoes now?"
That would have been a very good question to ask before expelling them. Similar questions might well have been asked before France's persecution of the Huguenots led them to flee in the 17th century, taking many productive enterprises from France with them.
Twentieth century examples are too numerous to cite.
Good Things have costs, often costs out of all proportion to whatever good they might do. But notions like trade-offs and diminishing returns seldom deter zealots, whose own egos are served by their zealotry in imposing their vision, however costly or counterproductive it may be for others.
The whole environmental extremist movement is based on doing Good Things, in utter disregard of costs or diminishing returns.
The idea that DDT might leave residues with harmful effects on the eggs of some birds was enough to set off a worldwide environmental crusade to ban the use of that insecticide. The resurgence of malaria after that ban has cost millions of human lives.
Green zealots are not about to reconsider, on this or a whole range of other issues. Their vision triumphed, their superior wisdom and virtue were affirmed, and that is what it is ultimately all about. To admit, even to themselves, that their ego trips have cost other people their lives would be too much.