Many countries have no issue with that, serving time is considered enough of a punishment. The idea of (especially mandatory) deporting of criminals is relatively new, driven primarily by the far-right.

IMHO it is unethical for two reasons - first, it violates the principle of every human being equal under the law because clearly non-citizens have a second punishment on top, second because in many cases (although not in this one) the target country isn't equipped to deal with serious criminals - that's how the US got MS-13 and other gangs causing trouble in South America in the first place.