I have a take on this that I think no one will have fun with:

In my opinion there is no moral way to keep a cat as a pet.

Allowing cats to roam as they desire results in the aforementioned ecological damage. The opposite - keeping cats locked in a few thousand feet at best for twenty-odd years of life - is cruel.

As someone who was raised in the woods with outdoor cats and couldn't imagine keeping them inside - even though we lost two as I grew up - it's a circle I just can't square. So I figure that if and when I get cats, I'll dodge the question and adopt some older cats who were already raised inside and couldn't be trusted to go outside safely anyway.