If nests are removed the swallows are not destroyed, they would build elsewhere. We live in Farm land and I have seen this happen when swallows build over front doors or entrances to barns etc., The Farmer gets a hose as soon the the nest is being bulit and when the swallows go away from more building materials, the Farmer washes away the nest foundations. This is done a few times and the swallows go elsewhere, there is no cruelty or death involved.