With all due respect, I don't think that your son in law (wonderful lad though he may be) or your neighbour are proof of your sweeping statement that pigeon fanciers kill more of their birds than predators. It will take something a lot more scientific or statistical than that to convince me.
Hey. I've held my hands up and admitted on a public forum that in my hobby culling of no hopers goes on, and if the figures were published the numbers up and down the country it would be horrendous, but as I have stated it's not shouted from the rooftops, and indeed it is denied as the public face has to be shown as a caring one.
I have known many Pigeon fanciers, and I will, with hand on heart say that all the ones I have known carry out culling of their birds some for health reasons but also under performers. It makes economic sense, or else there would be lofts full of dross with no value and no line of excellence, if they bred the strength of the offspring would also be diluted, and pretty soon the hobby would be in disarray.