Like I taught my kids, everything is basically food for something else, and unwatched housecats left to run loose & free are like low hanging fruit for predators.
If you don’t want your cat to be kitty food for a big kitties, don’t let it run wild.
A couple of years ago, our neighbors watched in horror as a hawk snatched their six month old Persian kitten right from their back yard in front of them.
I wonder what kind of illogic you know who would use to argue that the mountain lions carry diseases and don't belong there (much like the native birds she wants the non-native house cats to wipe out).