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Very rarely do modules fail to install.
Not true on my planet. I'm astonished at how often even simple modules fail to install (for me and for others). I'm staggered at how much effort and code has gone into addressing the installation of modules -- and yet most resulting systems that I've tried fail about as often as they succeed and even the most reliable (perl Makefile.PL + make) fails all too often. And I'm astounded at how quite a few complex modules can be nearly impossible to install.
Maybe your view on this is because you've been blessed with exceptionally "vanilla" systems (just a wild guess).
I avoid non-standard Perl modules much of the time, in part because even when I can get a module to install, I very often find that it is unsuitable. There's lots of great stuff on CPAN and even more good, useful stuff on CPAN, and tons more stuff further down that end of the quality scale.
A total refusal to use modules is an all-too-common situation and I find it unacceptable. But I often avoid non-standard modules and I appreciate it when others realize there is a price for using a non-standard module and that sometimes the benefit doesn't out-weight that price. Perhaps you've already downloaded and installed the module (and maybe didn't have any problems doing that) and have read the documentation and figured out its quirks and found that it works well the way you use it and remember enough, but for a non-standard module, most people will still have all of those hoops to jump through.
But I also now realize that I wish more people would pay attention to the 'cost' of using a module (especially a non-standard module or a module that won't work on slightly-old Perl versions). There are still plenty of cases where the cost/benefit is a no-brainer in favor of using the module (for me, sending e-mail from Perl would be such a case). And I consider "no modules" to be an unreasonable stance.
But, "just do use Date::Module; ConvertRoutine(...)" sure looks easy, and probably is really easy for the person who writes it. But I usually find that it isn't very easy. Perhaps because I must be convinced that it really does solve my problem before I'll use it, and one test doesn't convince me.
So let's have some balance on the scale of "use modules".
*shrug* All I really wanted to say was the first sentence. (: