I've been thinking about why it is such a headache.
Attempts to impose systems that enable characters to use charisma to have an immediate, direct effect on the dealings of others, principally by players against non-player characters, has largely failed. The tendency of players is to see NPCs not as believable entities, but as tools towards an end ~ and thus, charisma is used as a weapon to dominate or coldly manipulate guards, officials, common persons or enemies into a state of obedience and submission by virtue of a die roll. Given any chance that this will work, without any real consequence experienced by the player, the player is bound to try again and again, like pulling a slot machine, addressing each NPC with the expectation that the roll will work, so that this time, the character-victim will instantly become the player’s vassal.
This suggests that die rolls cannot work. However small the chance for success, the player will always go for it; and supposedly, the high-charisma character should have a fairly decent chance of winning over strangers and influencing people. Without a consequence, failure to do so is fairly meaningless; and what consequence can we provide that will mean something to a player outside of the NPC immediately taking up arms?
We can leave interactions to role-playing, insisting the player win every success through parley with the DM ... but then we're forced to accept that the NPC is always the same person, with the same likes, dislikes, buttons, prejudices and recognizeable behaviour patterns. However much the DM might try to take on another personality, we're still going to the same well and, ultimately, that well is predisposed to allow success or impose failure based on the DM's agenda.
In effect, the player character is a psychopath. Because charisma is used as a tool, the expressions are glib and superficial. The PC is bound to have a grandiose and exaggerately high estimation of self with compared to NPCs. The PC feels no resistance to lying, cunning or manipulation of NPCs. If an NPC dies under the player's watch, it is easy to lack remorse or guilt. Players are generally very callous towards NPCs and rarely possess empathy for them. Players casually kill NPCs without notable impact on their self-identity. Players are overly impulsive, particularly in their dealings with NPCs. They will usually objectify NPCs, seeing them as possessions. And so on.
None of this really matters, because NPCs are fictional objects and the players know it. It requires an enormous build-up of a particular NPC to gain a player's concern or empathy for that fictional character ~ and some players will simply refuse to invest themselves personally in something that is "just made up." It is a challenge that has frustrated many writers for centuries, in having to deal with readers who insist on treating film and literary characters as "not believable" for a host of pejorative justifications. These range from not liking strong women, superheroes, drug addicts and other criminals, the presence of intelligent black people, anything verging on a racial stereotype, LGBT issues, anything suggestive of weakness and, of late, a pronounced dislike of cultural appropriation. "I hate your Egyptian character because you're not Egyptian."
Whatever the motives, players often won't adopt a sense of wrongdoing when using their 18 charisma to flat-out exploit NPCs, wringing out their last hit points dry before casually leaving them to face the dragon while the party beats a hasty retreat. So it is crucially difficult to create a game system that doesn't detrimentally empower characters with high charisma (leaving those with low charisma to shut up while the beautiful people talk), while encouraging the abuse of NPCs while vastly reducing the immersive qualities of player/NPC discourse.
What's needed is a consequence that doesn't depend on the nuclear option. At low levels, it's enough to make one NPC draw a weapon to discourage a player from getting too bossy, but as the levels climb it's necessary to have the whole tavern draw weapons, followed by the arrival of a substantial city guard, two or three knights and a local mage, half the town and perhaps a good portion of the kingdom eventually, because a 19th level fighter took it in mind to bitch-slap a fictional 14 y.o. servant. It gets a little ridiculous.
We humans, of course, don't act like psychopaths, in very small part because of the legal consequences involved but because we would feel awful for long periods afterwards, even our whole lives if the choice to do something really selfish and vindictive caused us to lose a friendship or question our legitimacy as likeable human beings. Guilt is a serious consequence; and not something that players feel overmuch.
Guilt can have serious physical and mental consequences. It can lead to headaches and stomach aches, muscle tension, lack of sleep, feeling on edge, feelings of desperation, self doubt, anger, overcompensation and a tendency towards suicide. In game, these are all measurable responses, none of which require an NPC to draw a weapon. In fact, they will tend to manifest because the player was successful in their manipulation, rather than the contrary.
Of course, players want to be free to be as evil as they like, without consequences. There's enormous fun in teasing small fictional children to fall out of windows to their deaths and pushing an unsuspecting townsperson into the open to "see" if the enemy has bows or not. What evil female character hasn't pretended to be a prostitute long enough to lure a client into a private place in order to assassinate them and pick up a few coins?
If we impose a guilt rule on such persons, what then? Where's the fun? And in what ways are we challenging the principles of player agency?
I'm not sure there's an answer for that. It may be that player characters must be self-declared as creatures immune to guilt, a condition that cannot be possessed by characters with a charisma above a certain point. Someone will inevitably argue that Hitler had a charisma of 18, but I'd argue there's no measurable evidence of the assertion, and that our mythology of his charisma is due to our needing to explain the irrational willingness of the German people to embrace him into their hearts. When I look at the little corporal with his silly mustache, stomping and strutting, and hear the words of his speeches and his manic delivery, I don't see this "charisma," though I do see a certain drive and intellect in his unbridled ambition. Accounts of Hitler in the 1920s don't bear out this "charismatic" argument, but it is clear that he was loud, irrepressible and willing to surround himself with gangsters, whom he then organized and empowered through his ruthless strategies. We know that the crowds of "adoring" Nazi synchophants were populated with gangsters who did not hesitate to club and beat those who did not show enough sychophancy. It is probable large parts of the crowd attended in order to be seen by their neighbors and therefore not called out as traitors to the state, rather than any appreciation for a maniacal racist megalomaniac. The charismatic theory has some considearable holes in it.
But ... we're only interested in game procedures, at any rate. If we regulate evil persons out of the exploit-through-charm option, and if we impose meaningful repercussions upon players who use charisma in order to callously exploit NPCs, reducing their constitution, wisdom, ability to rest or their ability to be fully charismatic for temporary periods, or even potentially permanently, players might hesitate to use their 14+ charismas as a "let's fuck over everybody" game strategy.
I wouldn't think it would be popular. Quite a number of players, used to acting as assholes towards NPCs and shrugging it off like a speck of rain, will chafe at the notion. It would probably be embraced only by players who already don't want to use charisma as a weapon. The idea wouldn't be adopted at tables run by DMs who actively encourage players to lack empathy or concern for anyone except their selfish selves ... so long as they pay fealty to that DM.
Such a rule, however, would be constructive in causing a player to hesitate before flashing a smile, winking, and suggesting the princess betray her father, her people and her virginity, so that she can run off to a life of adventure with this gorgeous adventurer whose going to dump her in the next kingdom over as soon as the quest is complete.
A player might, then, feel a little bit bad about doing such things.