Well — it (changing a nation’s mindset) can sometimes be done, and has been. Post WW2 Japan, for example. But to do it you have to beat the population to a pulp, and probably have to demonstrate willingness to use even stronger measures (nukes, in the case of Japan.)
Modern Western sensibilities make this unacceptable - at least for now. When we lose a city, or generally suffer significantly, that may change.