An interesting line of argument developing here, but as someone who lives next door to a dotty woman who takes in stray cats, I do have some sympathy for ethandron. At the last count she has around 5 or 6 cats, and as we have none, they head straight for our garden morning noon and night to crap and generally use our lawn as their litter tray.
I believe that as usual, the problem here rests solely with the politicians and the law makers in this country. Crap is crap no matter which animal it originates from, and all dog owners are legally liable and responsible for their animals waste. So why is cat poo any different or less offensive than dog poo?