I like birds too. But cats kill birds — that’s nature. The smarter birds will learn to keep clear of them, and then pass on their genes. I wouldn’t worry about a lack of birds visiting your property due to cats.
That said, if feral cats are pests on my property, I’d have no qualms about shooting them.
Some neighbors cat at my bird feeder dont get the message of a Crossman at 2 or 3 pumps may need to up it to 4 or 5
Owner, whoever they are, may get the message after picking one of those festered things out.