Stray cats are exotics in most parts of the world and therefore fit poorly in the ecosystem. This is a problem for both the cats and the nature around them.
One of the most harmless ways of preventing stray cats is by taking good care of your cats and neutering them. The less kittens are born, the less cats become homeless.
Neutering also has health benefits as prostate problems and ovarian cysts do happen a lot when cats get older.
In 2017 Feral Cat Day became Global Cat Day instead.