I don't wish to join the debate either but i find myself thinking like longdogs on this subject. The bottom line is most people don't give a shit, out of sight out of mind, if someone from the public was randomly selected to view the death of every healthy dog that was put down whether they liked it or not things would quickly change.
The same happens with cats, all my mum's cats have been rescue cats, some people working with the CPL will turn their own homes into cat sanctuaries and do all they can to rehome them. The people who go out of their way to look after the welfare of unwanted animals are saints in my opinion.