Except the bank has a laid down policy against using crypto or gambling with it, I think that it's unfair to fire the worker because he gambled with crypto. Perhaps there's more to the story but if it's just him gambling with crypto, especially not doing so during work hours, then there must be something wrong somewhere. Perhaps the bank prohibits their employees from engaging in gambling, not specifically crypto gambling alone, then it'll make some sense. There's no competition between cryptocurrency and fiat currencies so normally the issue of bankers holding or spending cryptocurrency shouldn't be an issue.