Saying that your building kills more birds than your cats do is like saying heart disease kills more people than cancer. Both are terrible and something needs to be done about both. Outdoor cats is not good for the cats or the wildlife, especially songbirds. They have decimated many populations of birds and there are a lot of studies on it. I also agree that many of these buildings need to do something to protect migrating birds. It's also a problem.

If you don't care about the wildlife there's the issue of the things that can happen to your outdoor cat. It's not healthy for them. Then there's the issue that you can't keep a cat in just your yard. Is it fair that your neighbor should have to put up with your pet in their yard? I'm sure if their dog was in your yard you wouldn't be too happy about it. Why should it be any different for cats?

And in case anyone thinks I'm a cat hater, I have 2 cats.