But it does beg the question that if a characters thoughts and actions are both controlled by mechanics, what is the point of "roleplay"? For example, if the DM says "you believe the merchant is honest" because they rolled high on their deception, that still doesn't mean I will buy the colored water he is pawning as potions of healing. And if you tell me I have no reason to believe the huckster is anything but honest, you basically have taken away the ability to play the character in a way I see fit.
I have a very finite limit on what I deem acceptable when it comes to influencing my character. You can give me as many carrots or use as many sticks as you want, but my declared action (or my characters beliefs) are decided by me alone unless overt magical powers overrides that. You don't get to tell me that my character feels afraid or gullible or compelled to run up to a armed warrior black ninja style. You can give me super disadvantage and force me to take psychic damage if I resist, but I want the option to resist. Otherwise why am I playing a character rather than a pawn in a board game?*
* I remember once playing the Game of Life with some kids in the day care I worked at. At one point I was deeply in debt and drew the card that said I bought a helicopter. My brain initially resisted the notion saying that there is no way I would buy an expensive item like that while in debt, but I realized it's not supposed to represent a rational person acting, it's a random chance mechanic disguised as a real world action. So unless D&D is supposed to exist on the same level of logic, I refuse to buy a helicopter regardless of how well you roll on persuasion when I'm already deep in debt.