The problem with this is that the US is notably one of the worst countries to let a cat outside, but because the US dominates the western internet everyone who speaks English gets scolded for leaving a cat outside even if if they have other bigger local environmental problems to solve instead.

Personalty for my local area i would much rather have we stop having grass gardens because there is a lack of diversity of local plants, or to stop driving cars because roads are creating floods.

Ethical reasons.

Also if you want something environmental, commonly used types of cat litter aren't biodegradable and cats with free outside access don't need any.

Oh and cats are also far more likely to kill birds that are already in some way impaired by something like old age or sickness, so while the impact is undoubtedly there, the numbers may paint a worse picture than reality.

And they also kill rats which in most places is a positive.