Of course small is subjective, but I would consider, say, a 1 in 3 chance to be small in this case.
>test for ethics is entirely asinine, as it renders anything of sub-infinite scale unethical
I don't see how this is so. Explain?
>anyone who chooses not to have children is behaving unethically -- as is anyone who has children, for that matter
This is also not obvious. Of course tenable is poorly defined, but there is nothing contradictory/chaotic/unsustainable about everyone stopping having kids. Furthermore, it is not obvious to me that the statement "it is unethical to not have kids (if you're able)" is necessarily absurd.