I am posting this as an example of a "risk that is widely perceived as tolerable." Is it high risk? I think so, judging by all the other examples of non-native animals destroying parts of ecosystems.
It is hard to predict how things like this extrapolate. But that is how it is -- we are more likely to observe consequences and infer the origins, and extinction around the world is a pretty big one. The evil cats scenario is just one from that article.
A snippet: In the street where I live, there are more cats than people!
And that is a problem. All those cats catch lots of birds and mice and rats and butterflies. Biologically speaking, cats are eating a huge hole in the food chain. No, seriously! According to several alarming reports, this is exactly what is happening in countries like the United Kingdom, Sweden and my own country, Holland. Bird species are vanishing, mouse subspecies are going extinct. All because of Molly, and Lizzy, and the other many billions of domestic cats that inhabit the planet today.