"Burke ever held, and held rightly that it can seldom be right … to sacrifice a present benefit for a 
doubtful advantage in the future ... It is not wise to look too far ahead; our powers of prediction are slight, our command over results infinitesimal. It is therefore the happiness of our own contemporaries that is our main concern; we should be very weary of sacrificing large numbers of people for the sake of a contingent end, however advantageous that may appear…
doubtful advantage in the future ... It is not wise to look too far ahead; our powers of prediction are slight, our command over results infinitesimal. It is therefore the happiness of our own contemporaries that is our main concern; we should be very weary of sacrificing large numbers of people for the sake of a contingent end, however advantageous that may appear…We can never know enough to make the chance worth taking…
There is this further consideration that is often in need of emphasis: it is not sufficient that the state of affairs which we seek to promote should be better than the state of affairs which preceded it; it must be sufficiently better to make up for the evils of the transition," - John Maynard Keynes, Burke's Timidity on Embarking on War (unpublished manuscript, ca. 1906) quoted in Robert Skidelsky, John Maynard Keynes: Hopes Betrayed (vol. 1).
(Thanks to a reader.)