The fact that when they are nuetered, it stops the breeding, but it doesn't stop them killing wildlife.
This method can only lower numbers, never eradicate them completey, the number sheer number of feral cats around basically means the only way to eradicate them is to kill them.
Say you neutered 1 tom, it would stop 1 colony from breeding. for this to happen, they would have to trap it, which would be difficult enough as it is. But that cat, could potentially keep killing wildlife for another 10 years, as could could the cats in it's heirem. Who is to say, that the tom they neutered would be the dominant male for that long anyway, unless they desex every single feral cat out there, you need a measure in place to still kill them.
Nuetering will work, but only in conjunction with shooting. I suggest you know what you are talking about before argueing Jordy, stick to consoles.