At the absolute minimum, I would expect any person claiming to be "good" to feel extremely guilty about interacting with soul coins in any way other than breaking them to free the soul inside. Certainly, using them as actual straight-up currency would be abhorrent and only undertaken in utter desperation, e.g. "we absolutely NEED this artifact in order to save the lives of hundreds of innocent people, and we've tried every other option except soul coins."
Lawful Neutral? Yeah, I can totally see the coins being seen as a distasteful but tolerable form of currency. Any Good alignment, though, I as a player would feel at least extremely annoyed if I was strong-armed into a situation where I absolutely had to deal only in soul coins, it would definitely feel like a betrayal of the character's morals and principles.