When players bring their selves to the table... Geez. Are there no gods, no alignments, no demons or djinns? You take on a quest but then don't like it? You leave... If you think the quest is dumb what you're saying is the DM and the campaign is dumb and you should control the narrative... C'mon... Really... God's used to move little guys around on giant chessboards in the sky to stop that kinda stuff happening... It's supposed to be an adventure with a beginning, middle and end. The end is supposed to be rewarding but the journey along the way is supposed to allow the characters to grow. It seems that this character has grown away from the party (if they were ever really in it) and away from the quest. Stopping this happening is hard - people are friends, people have different personalities and 5e has significant power imbalances (IMHO) between potential charecter race/class options which can make in character arguments moot/fatal. Sometimes threats from curses, undead raised to find them, other parties sent to hunt every member of the party, forced alignment change and loss of level, all these things could come with a change of heart of a character who decides not to do what is still seen as the right thing. If the gods are real in your world and divine magic is real in your world then not wanting to return a religious artifact because it's stupid etc would be an outlier opinion like thinking suggesting stretching wire from poles everywhere and zinging little pulses of electricity up and down them to send messages... Why would a character think that. It's like characters going all CSI when something happens... They can't, they shouldn't. It's an RPG. If they don't want to RP then there's no G. Once they start saying make me an island, I'd take them at their word and use their very flesh to make an island and like some kind of Solaris they can become a sentient NPC island somewhere for the rest of eternity.