Why is it that girls insist on saying “my girlfriend told me…” (in a Platonic sense), and not just friends? Yet, as far I have seen, guys simply have friends. Ahs anyone else noticed this? And, from my observations, this goes back before the start of the whole, slang “you go girl; girlfriend” t’ang!
Is it too much to ask that they just simply have friends?
It’s just one of those little speech mannerisms that doesn’t do any harm, so what’s the big deal? One of the things I’ve noticed about it is that it’s often used to distinguish between male and female friends, and also to distinguish between casual friendly acquaintances and close friends. I’ve also noticed that it tends toward being a regional sort of thing, like keeping pop in the icebox instead of keeping soda in the fridge.
I admit, I sometimes use that construction myself these days. When I’m talking about the woman who was my best friend all through high school, and is still my closest platonic friend, I’ll sometimes call her “my best girlfriend.” She’s not my best friend anymore; my husband’s been my best friend for quite some time now, and although people would know what I meant if I referred to her as my best friend, it wouldn’t feel right to me.
Hey, you’re right! I’m insanely jealous of all these women. I don’t even have one girlfriend, and here just about every woman on earth is constantly going on about her dozens of “girlfriends”! 
It does harm to the extent that it causes confusion. Not like anyone’s ever died because of it or anything but I do find it somewhat annoying for heterosexual women to refer to their female platonic friends as their girlfriends.
It’s like this:
Girls have boyfriends
Girls have girlfriends
Guys have girlfriends
Guys have buddies
It’s the way it’s always been.
“Boyfriend” was once used by some people to mean a friend of another boy, exactly as we’d say buddy or friend today. When I was a kid I remember my grandmother asking about my “boyfriends”. I didn’t like it and it wasn’t normal usage even then, but allowing for her age maybe it was normal when she was a kid (< 1910).
You forgot one…
Girls also have friends, as in “Can we just be…?”
It only causes confusion (mild confusion that could easily be remedied with a single question, at that) if you’re using it as a barometer of someone’s sexual orientation. By your own admission, it’s not a very reliable indication, and why do you care about a woman’s orientation anyway? Aren’t you gay? And isn’t someone’s sex life really none of your business?
The word has multiple definitions and connotations, just like gay, straight, love, sex, vanilla, and about a million other words. Until large numbers of women started living openly as lesbians, it was automatically assumed that a woman’s girlfriend was a platonic friend. Maybe you should get annoyed with lesbians for co-opting the word.
Okay, I use the word. I’m heterosexual, and I use it to refer to my female friends. I use it because I have a lot of male friends as well, and usually whatever kind of anecdote I’m relating needs the gender specification to make it funnier. For example:
“My friend got drunk last night and tried to hump a gumball machine” is much funnier when it’s “My girlfriend got drunk last night …” etc.
For the record, my male friends rarely get drunk and try to hump things.
I use it because it clears up confusion. My best friends are 6 girls and 2 guys (I’m only dating one of them).
~M