Stiletto
On the other side of the road
My impression is that your neighbour is Spanish and you are not. Please correct me if I'm wrong, but, if this is the case what you have are two very different cultural attitudes to animals.
Rural Spaniards generally do not castrate cats, nor spay them either; this is their "normal". Ditto for dogs. There are a lot of people who won't take them to the vet either, not regularly anyway. Some are better at treating them at home than others and often flea/tick preventatives aren't considered. It's a spectrum and your neighbour may be in the mid to low range. Although there is a change (towards UK/central European sensibilities and practices) it is slow and starting in cities and towns, where people are keeping animals as pets.
Bear in mind that in Franco's time, often there was barely enough food to go round for the humans; animals were expected to forage and/or live off left-overs. I remember speaking with a ~90 year old man who told me that back when he was a kid/young man, people didn't bother burying a dead dog. He was commenting with bemusement on how "the English" treat their dogs.
So, while I don't imagine your neighbour is that old, he'll have been raised by parents from that generation. What you are describing, is what he knows.
He is right, chickens from local stores often have their beaks cut.
I can understand why he wants birds with intact beaks.
Personally, I wouldn't give your neighbour a puppy or a kitten either, but there again that wouldn't be an issue because I neuter my cats, female dogs and potentially problematic male dogs. As for chickens, I think I'm more accepting of losses to predators than you are. I've actually refused to give someone one of my roosters because he wouldn't have (what I consider) enough freedom! I don't have fertilised eggs but if I did, I don't know what I'd do in your position, TBH.
That's me though and as other posters have said, this is your decision.
Notwithstanding, I do urge you to consider:
Although he'll probably get eggs/chickens anyway, I do understand why you would not want to give him eggs from your chickens. Also, I'm curious; do you eat meat from conventionally raised animals?
I wish you wisdom, peace and balance to help with your decision-making.
Rural Spaniards generally do not castrate cats, nor spay them either; this is their "normal". Ditto for dogs. There are a lot of people who won't take them to the vet either, not regularly anyway. Some are better at treating them at home than others and often flea/tick preventatives aren't considered. It's a spectrum and your neighbour may be in the mid to low range. Although there is a change (towards UK/central European sensibilities and practices) it is slow and starting in cities and towns, where people are keeping animals as pets.
Bear in mind that in Franco's time, often there was barely enough food to go round for the humans; animals were expected to forage and/or live off left-overs. I remember speaking with a ~90 year old man who told me that back when he was a kid/young man, people didn't bother burying a dead dog. He was commenting with bemusement on how "the English" treat their dogs.
So, while I don't imagine your neighbour is that old, he'll have been raised by parents from that generation. What you are describing, is what he knows.
He is right, chickens from local stores often have their beaks cut.

I can understand why he wants birds with intact beaks.
Personally, I wouldn't give your neighbour a puppy or a kitten either, but there again that wouldn't be an issue because I neuter my cats, female dogs and potentially problematic male dogs. As for chickens, I think I'm more accepting of losses to predators than you are. I've actually refused to give someone one of my roosters because he wouldn't have (what I consider) enough freedom! I don't have fertilised eggs but if I did, I don't know what I'd do in your position, TBH.
That's me though and as other posters have said, this is your decision.
Notwithstanding, I do urge you to consider:
- the importance of good neighbourly relations
- that if you do decline, to do your very best to explain calmly and as non-judgementally as possible (!) why you don't want to give him fertilised eggs and why it matters so much to you
Although he'll probably get eggs/chickens anyway, I do understand why you would not want to give him eggs from your chickens. Also, I'm curious; do you eat meat from conventionally raised animals?
I wish you wisdom, peace and balance to help with your decision-making.