Everyone could get caught off guard on things he's not aware of once a while, be it pure or toolkit. Regex bites people on a regular basis.

Whether one writes in pure Perl for the sake of portability and such is a bit like a quality control or risk management question.

Using your case, File::Copy might seem less advicable to a sysadmin working on a multi-OS environment than someone who just uses it for productivity tool on his own desktop. The former is more likely to get bitten than the latter and therefore "pure Perl" will be a more immediate concern.

For the latter, who rarely works on other OSs or even other machines, worrying about portablity and such is like buying a typhoon damage insurance when he's living in Canada.

VB programmers apparently don't concern themselves with portability and such issues, as they apply themselves to a restricted enough environment. On the other hand, a Java programmer may need to be concerned about the issues.

Whether someone should be writing in pure Perl partly depends on the risk for him for not doing so. If the risk is low, one might feel, why spend the extra time on the "5%" when he has covered the "95%"; it might seem counterproductive to spend the extra time to deal with things that almost never occurs to him. However, when the risk is high and someone ignores it, it's reckless.

So, cliche as it sounds, pure Perl vs toolkit is not a binary choice but more like a calculated bet. If a toolkit save someone more time than the time he fixing it, why not use a toolkit? But if the reverse is true for him, long live pure Perl. (Of course, sure many other people will look at the issue from other perspectives as well. It's a healthy thing.)