I live on the edge of 10k+ acres of wilderness. Our 2 cats are indoor/outdoor and always will be. They are of course part of the food chain, and are as at risk as any bird, lizard, gopher, mole or snake in the neighborhood (if you want to call it that). Our cats usually shit in my wifes favorite flower pots, as do other cats in the area. I'm sure our cats also crap in other peoples yards, but nearly every cat we have ever had or seen buries their shit. We have mountain lions, bobcats, deer, skunks, raccoons, herons, hawks, squirrels, you name it on and around our property. Not really seeing how our 2 cats do not fit in perfectly. We do bring them in at night because that is prime hunting time for mountain lions. And yeah, we have had a couple cats disappear over the years. That's just how it goes.
So, while we may be the exception, I'm not really interested in hearing how our cats are an environmental hazard to anyone or anything. YMMV.