"Act only according to that maxim whereby you can at the same time will that it should become a universal law."
Kant's categorical imperative is wrong. There are plenty of things which it is acceptable to do, but which wouldn't work if everyone did it.
If I create a small bit of pollution, but I know that I am unusual and most people will not create the same type of pollution, then I can reasonably suppose that the total amount of that type of pollution will be below the amount that can be "absorbed by the earth".
A Catholic priest is celibate; does not have children. However, he would regard a world in which no one had children, to be sub-optimal. This does not show that he is behaving immorally by not having children. He can remain celibate because he knows that most people will not do so.