Lanefan, you are at least putting forth an argument, which I take to be something like (correct me if I misrepresent):
1. There might be instances where players might take a low charisma yet also want their character to be very physically attractive.
Which is fine provided those players are willing to play the character as a boor, or anti-social, or offensive, or in some other manner that balances out those good looks and make the poor-overall Cha score make sense. I've seen this done, and done very well.
But when your character's Cha score is 8 and you're playing it as if it's got James Bond-like levels of suave-ity and hotness (and expecting the same results) there's a major disconnect if not outright bad-faith play going on.
2. This is a problem because some of these same players might expect to get actual in-game advantages based simply on their character's physical attractiveness, despite a low charisma.
My first question is: what makes charisma different from any of the other abilities in this regard? Indeed, isn't the prime culprit for this sort of behaviour Intelligence, not Charisma? Players are forever taking Intelligence as a dump stat yet playing their character as a super sleuth or whatever.
Yes, and IMO this is also a problem.
My second question is: Where is the DM? When it is time for a charisma check, say to try to influence an NPC, physical attractiveness does not affect the roll. So if that player tries to claim an advantage for their role-play decision to have their character be super hot, the correct response is "it doesn't work that way."
Indeed. It's nice, however, if the DM has backup from the rules-guidelines when saying that. That backup does not here exist, and a player who wants to root this argument in the reality we live in where good-looking people very often do get more advantages is (unfortunately) on to something.
To me, this is similar to a player claiming that their character comes from a really wealthy family and therefore receives a weekly stipend of 100 gold, or comes from an ancient line of warriors and thus starts with a legendary weapon that has been passed down.
Which, given how 5e backgrounds work, is also a gray-ish area. Fortunately, starting-wealth rules/guidelines serve to nip this specific idea in the bud, but the nobility or family-wealth/influence angle can be played for advantage in many other ways. This is why I have it that one's past profession (which can include nobility) is either something chosen from a very basic (and boring) list or randomly rolled from a more extensive one. Family background is also subject to randomization if one is looking to gain advantage from it - you're free to choose that your family are peasant farmers but not free to choose they're wealthy merchants with contacts in every town up and down the coast; if that's what you want then we'll roll for it, and if the roll comes up as peasant farmers then that what you get.
All this is somewhat intended to reflect the luck of the draw in what sort of lifestyle or social strata one is born into.
The game just doesn't work that way. You don't get to give yourself in-game advantages just based on your character description.
I agree with this. Thing is, in some cases there's rules or guidelines in place to enforce this and in other places the DM is kinda left hanging.
Unless the DM wants to allow it, which trumps everything else.
Agreed.