I've never done it before but we have found abandoned newborn kittens (from ferals) on our property a couple of times in the past. If I ever find them again, instead of the RSPCA this time, they will get a quick, humane death, be frozen for 6 weeks, and then I would have no problem putting them to good use.
I think that sums up my thoughts on the matter, I have no problem with cats kept as pets (we have 2 at my house, INDOORS!!!) but if they are running wild and especially if they're born in the wild, they are nothing more than a feral pest, on par with a cane toad!