You're right, leneeia, cats roaming free face many dangers to their own health and welfare.
(Some of those dangers are especially prevalent in urban areas, but even in rural areas there are some.)   I think those may be more the issue than the decline of bird populations, except in sensitive regions were some species of birds are threatened with extinction and also preyed upon by cats.    I still think the urban cats, as well as farm cats, provide valuable services to humans.