if you spend six months writing code that caters for porting to some non-forkable environment

That's not what we're talking about. It's a single line of code.

And if you were to ask if I would spend the literally 7 seconds it takes to type defined($pid) or die "fork failed: $!"; to save my employer the potential costs of a mysterious failure sometime in the future by replacing it with an error message, even on platforms where fork is supported, then yes, I would! I'm taking your continued disagreement to mean that you wouldn't. Although I disagree with that, I can't stop you from providing your employer with whatever code you like - but that's not what we're talking about either.

We're talking about providing a piece of code to help a stranger, and potentially many other future visitors of this site. In your posts, you showed the usage of fork without a check for an error or a mention that you've omitted the check and why. You can't be certain that on any of the systems where this code might be run in the future, fork will never return undef.