Stray cats and any house cats that are allowed outdoors unsupervised are a big problem. They kill billions of birds and small animals every year and have already contributed to the extinction of several species. Whether due to their predation or the diseases they carry the effect they have on native species and ecosystems is incredibly harmful.
If you have a cat the least you can do is have it spayed or neutered and vaccinated. Also be sure to keep an eye on your cat while it’s outside so you can prevent it from pouncing on any innocent native, and perhaps even endemic, birds or other environmentally beneficial animals like this poor Zebra Dove that was killed by a cat which was already over-fed but was just looking for something to play with/torture and kill.