I actually have to reply to this in two separate posts. Sorry, my ideas on each are too big to fit in one post. (MODS, I vote for sorting it into two threads. Your call on whether that's necessary.)
First, on the defining poly business:
There is a tendency to define poly as open AND sexual AND loving AND consensual relationships. Technically, this definition excludes polyfidelity (depending on one's wording), and relationships that haven't resulted in sex, and relationships that are pushing on mainstream boundaries of love (potentially including BDSM). It also includes
relationships that fit these definitions due to societal pressure (Mormon polygamists, for example), though Wikipedia's poly article insists that polygamy and polyamory are separate.
Personally, I have no problem with a clinically precise label, so long as we acknowledge that real life is rarely so straight-forward. For example: one of my life partners wants us to go polyfi, and I'm not having sex with my girlfriend, and my friend with benefits says "I know," when I tell him I love him, rather than replying in kind. Everyone but me in my constellation who is involved directly with more than one person (with full consent of all parties and usually a lot of love and sex, mind you) isn't sure the poly label applies to them... What does that even mean?
I'll admit, I've gotten a laugh out of AT's tag before. I feel like I know what she means by it: if you're swinging (ie "fucking around"), you're not poly. The pun in "just fucking around" implies both that you're having casual sex and you're wasting your time. Thing is, I'd argue that that's more than "accuracy in description". I feel comfortable saying that that pun is there to be read into, and insisting that it has no other meaning is skirting the issue.
Here's where I get irritated:
Casual sex is an all together different topic and idea than polyamory. Fact.
Fact: RPC, I suspect you do not personally hold the answer. Poly and casual sex share some common elements, and real people who are going outside the mainstream on the monogamy front are likely to confront both. What do we do when the line gets blurry?
What about the Kerista commune, where the term compersion was invented, and thirty-something people were all married, having sex with opposite-sex partners on a schedule? I'd call that married casual sex myself, having at least fifteen partners and no choice about which one to sleep with-- not much different from key parties. (Yes I'm being controversial on that stance, and it's deliberate.)
How about my beloved friend with benefits... I've been his confidante for years, and now he's my live-in lover, but he chooses not to say 'I love you'? If he's in our communal kitchen baking brownies (with ingredients we bought together on a shopping trip) before he and I get alone time, but he claims it's not about love and I'm okay with that, how do we draw that line?
If we can't talk openly and honestly and politely on here about how to navigate this stuff, I'm not honestly sure where we all ought to go... So I say there's nothing wrong with being asked about our word choices on the internet, as a reminder to be courteous and open-minded--- There's backspace and delete and preview post for a reason.