So, my question boils down to: is it a bad idea to have global variables?

There are several answers to your question. Let me just give a few remarks.

• First of all, "global variables" is not a term everyone uses to mean the same thing. Many Perl programmers use the term "global variable" to mean "package variable". But in general, a "global variable" means a variable that's "visible" or "accessable" from everywhere. A lexical variable defined at the file scope can also be a global variable.
• Perl 1, 2, 3 and 4 didn't have lexical variables. Or name spaces. All variables where global. Was Perl evil then? I don't think so.
• "Global variables bad; non-global variables good" is an often chanted mantra, but it's an incorrect one. What is considered good programming is to have variables with a scope as small as needed. And that when you can use a lexical variable instead of a package variable, the lexical is usually preferred. Note that this does not mean every global variable is bad - it's not a rare occasion having a global variable that is appropriate.
• Whether you use a global variable or not usually doesn't have much impact on speed. And if it does have much impact, it's often caused by passing large variables into subroutines in such a way that copying happens; if that's the case, globals may be a winner (although using references often reduces the need for copying as well).

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