I mean, I know why a warlock would pick a patron to go against - it gives the player some drama built-into their character if they know that eventually they're going to have to turn against the demon lord/archfey/Great Old One/Whatever that they have a pact with.
But where some folks run into problems with these kinds of things are when the DM is using the patron/god/oath/whatever to either create a story that the player doesn't want or to force the player to do what they want and are using an in-game measure to do that.
The unstated fact in the OP is that the DM is the one that is deciding what the Patron demands. If the character is defying them in an in character bit to further their own story that's one thing. But if the player doesn't want to do what the DM wants and the DM is using their patron to try to force the issue, that's a different thing entire.
So the question I would have is - why is this situation coming up at all?
If I have an issue with a player and their PC it will generally only be a few things. For example they're being disruptive, they're antagonizing other players to the point where it is not fun, they're dominating the game to the point where other players don't feel like they can contribute. This is a player problem that has nothing to do with their class.
If someone is not following the edicts of their god or patron, that's a roleplaying thing. I'll have a chat with them offline and we'll figure something out. Either they don't understand something, they have a motivation I don't understand, they want to change something about their character or maybe it's just not the class and character for them. I
won't punish them with in-game penalties because I don't think they're playing their PC "right".
The second paragraph is all hypothetical for me, it's never come up. I will occasionally warn people that, for example, I consider torture evil and I don't allow evil PCs. That's happened maybe once in the past decade or so.
I'll never force a story on a player, that's bad DMing. I'll provide opportunities. There will be repercussions for actions taken or not taken, both good and bad. If there's ever anything I'm unsure of I'll either hint at it to get a reaction or just discuss offline.
None of this has anything to do with specific character classes.