All of my cats live inside, so if a bird breaks in he is trespassing (and, thus, fair game).
I have lived with cats most of my life, all indoor cats, all lived to advanced old age, and I can't recall a single case of bird victims or even feathered evidence.
The cats do get daily outdoor privileges under supervision, but the birds seem to have settled on a mutually beneficial schedule.
My cats never visit neighboring properties.
Perhaps they should concentrate on catching, spaying and releasing some cat owners.