The perennial problem for city legislators in any country, but I am referring to America here, is that if they want to deal humanely with feral cats and try and limit their numbers, they cannot allow the public the authority and freedom to trap and kill stray cats outside because any number of them may be domestic cats owned by an individual. Domestic cats are the same as any other possession and if they are killed by somebody that person has committed the crime of criminal damage and probably theft. In my view, currently, the only humane way to deal with feral cats is to employ TNR practices. The big barrier as my article linked to above suggests is that you cannot differentiate between a feral and domestic cat at a distance. Close up you probably can because often they are ear tipped but this is not always the case.