This is untrue and I have a hard time that somewhere in your heart you don't know that. As someone who had three feral cats show up the neighbourhood, two who were pregnant, and who adopted them all due to lack of space in the local shelters (for a total of 3+4+7!) cats, they were too feral, but in the process of being tamed, for a half year, and in the process of being training to not go outside at all for another year. I can tell you I dearly love every single one of those cats who are *now* securely inside and spaid/neutered, but who I prayed for every time they left our yard. Did I lose some to threats? Yes, two died as kittens to roaming rottweilers (who came on our property-- would it have been fair to kill those, too?), two died to cars, and two disappeared. Did I grieve horribly every time this happened? Yes, I did. If someone killed any of them, they caused me months of horrible grieving and poor mental health, and I still sigh and wonder what happened to my Mars and grieve over my Nova getting hit.
You raise chickens. These creatures humans have domesticated and bred to be the ultimate prey animals. We also domesticated cats to take care of small nuisance animals. Don't make the individual pay for a human or humanity's sins.
And talk to your neighbours and try to figure out a solution. We live in 2020, not the bronze age. There's no reason for such violence, especially if you let your *prey animals* roam around unguarded.
I applaud your kind heart & the time you invested in helping, taming, rehabilitating the fetal cats that you describe. I also applaud that you keep them contained so that they are safe/other creatures are safe from them.
As for would you be justified in killing a dog that wanders onto your property & kills a pet, that's a HUGE yes. The fact that you wouldn't & didn't do it is your choice.
My opinions & choices seem to be the polar opposite of yours & while that's fine, it's also irrelevant. This is a thread about "how would you handle..." not "Omg, convert that predator eliminator."
If we'd really progressed as far as you think then be it the Bronze Age, Golden Age or Space Age, people would respect others, take care of their animal companions and not be flaming jackholes all the way around.
But that's not how people are. When a pet owner opens their door to let their "cat be a cat" or because "well, a dog's gotta roam," I already know how stupid they are & don't need to have a conversation with them to prove it...let alone waste a perfectly wonderful dozen of eggs on them.
If you don't like it & you wouldn't do it & your neighbors are responsible, I am ALL about you doing what makes you feel best. Given your story, I see that's not exactly the case.
Eliminating any & all threats to my girls is my responsibility. I don't have prey animals, other than chickens. They are securely kept and supervised when they're out.
I am all for letting people do their own thing, as long as it doesn't negatively impact me. I give a wide berth to what I choose to avoid but I do not run & I don't ask for permission to keep my property and family-chickens included-safe. And I don't "know in my heart" that not doing it your way is wrong. I know quite the opposite, actually.
And while I know that not everyone can or would even if they could, I loved someone else's idea of a cat enclosure with lots of safe places for them to roam, hide & explore.