If you had a dog would you not clean up its **** when you took it out for a walk? Encouraging your cat to do its business outside is exactly the same thing. There are plenty of iffy diseases which can be contracted from the faeces of both so it should be contained appropriately. I'm sure you'd not be too pleased if your kid came running in with crap smeared on its face and eyes because your neighbour didn't care where its animal did its business.