In no way do I blame cats for killing birds, mice, snakes, frogs, salamanders and the occasional butterfly or dragonfly.
They are supreme hunters to their very core and blaming them for acting on that (whether it’s a real or toy bird or mouse) is as pointless and unfair as blaming a cougar for killing one’s dog or a deer for defending her fawn.
Research for many decades (from all over North America and Europe) has shown that death by a domestic cat is the second main reason for the decline of native bird populations. The first is loss of habitat largely from human destruction.
Since humans supposedly are reasonable and able to change their behaviour for good cause, then clearly the loss of habitat by us is to be deplored more than the cat’s decimation. That said, since cats are largely domestic pets, we should use our reason to prevent the damage they do, as we should be avoiding poisons that kill birds and other species, including cats that eat the rat that eat the … on and on. Cats, by the way, eat very few insects and more in play than as food; some such hard-shelled insects can be injurious as well.
Spaying and neutering cats: a no-brainer, but it won’t stop Fluffy from hunting even if it’s only in the immediate neighbourhood.
Bottom line: humans can, and should, be doing much to reduce the drastic decline in bird populations around the world. Keeping cats from roaming free is one of the easier and very significant ways.