If you feed a feral cat, you take responsibility for that animal. Your assisting this animal's survival will have an effect on your neighbors and their pets, and on local birds and other wildlife. So, if you're the one feeding the cat, it ought to be your responsibility to see that it is healthy and that it has been spayed or neutered.
When I lived in the city, the woman next door thought she was doing a good thing by feeding feral cats. Ten cats took up residence in my yard, and I got to watch them toy with the lizards and mice and birds they caught. Finally, we convinced the woman the cats were a problem; and they were trapped and spayed or neutered, and the sick ones were euthanized. Within a few months, their number decreased and they were no longer a problem.
Cats are cute, but they're a big nuisance in large numbers. If you aren't going to care for them, please don't feed them.

-Joe-
(whose wife keeps three cats too many, but at least they're fixed)