In the case of the mustangs, the method you describe has obviously worked well. I would like to see something like this happen with the feral cats, only there are millions, not thousands, and the area to try to capture these millions is many thousand square miles of unpopulated desert. The only thing out there is Uluru. I'm not saying that efforts shouldn't be made to combat this problem in a more humane fashion, but the terrain has to be taken into consideration as it's the biggest obstacle in the way of progress in this area.
And yeah, Bruce, we'll never be able to shake our penal beginnings. But I don't want to, either. It's part of our history and a huge part of our history. But the criminals did not found this nation, and whilst I'd like us to break free of our British ties, and become a republic, apparently much of the Australian population does not agree with me, as a referendum held on this issue some years back (things might be different now) overwhelmingly voted against becoming a republic. Shame, but what can you do?