If this is the extent of your knowledge about what constitutes an adequate diet for cats, then please don't demonstrate your ignorance by posting drivel like this. A diet of [mercury containing] tuna or sardines does not contain certain vitamins and other nutrients essential for cats' health. And I'm sure that people who put out feeders to attract birds for them to watch would really appreciate everyone's cat turned loose to forage for its own food. Cat lovers would surely appreciate the fleas and other vermin brought back into the house and their cat exposed to diseases, cars, and internal parasites.
It seems the both of us have some research to do!