I've killed a few feral cats and I would say 90% of them were due to them fighting with my domesticated cat. The farm across the road was the big draw. Only one was memorable though, had a big tom cat that showed up only at night and wouldn't go into a live trap. I had to use a foothold to get him.Well stated as usual.
I would be willing to bet that the majority who choose to kill feral cats are not anti domestic cat.