Answer: could be both its up to you will explain each
Explanation: It could be both because if the cats aren't non native cats then that would not really pose a threat. Now let's say it's a different species then I would say it wouldn't be the best idea unless you can control the amounts of cats and send them back to their native country.
In terms of a disease it depends on the effects and if it would affect any other animals or even humans. But if it wouldn't cause any future problems such as a new diseases being spread to humans then I think it would be the safest option.
It is your opinion. I'm writing what I believe
Hope it helps