Why is giving the impression of doing something impartially, more important than actual improvement of the situation on the ground? Is it some sort of puritan fixation on punishment that I don't get?

Yes, humanitarian interventions are sold on the basis of the white hatted West riding to the rescue of poor oppressed underdeveloped helpless natives.  The Serbs made the mistake of being the dominant ethnic group in Yugoslavia and afterwards and rather over-played their hand by engaging in activities that were uncomfortably reminiscent of WW2.

The fact that Albanian/Croatian/Bosnian atrocities followed merely confused the simple narrative required to maintain popular support for expensive interventions and so were largely ignored - even when predicted and expected.

National boundaries have historically been determined largely by the outcomes of wars between princes and other rulers, often in a colonial context.  The problem is that since the 20th. Century advances in military technology and the scale of civilian casualties led to a search for another methodology, but there really isn't any mechanism in International Law for creating new states - as to do so, by definition, violates existing Sovereign boundaries.

Thus gross human rights violations, genocide and the implosion of empires are about the only proximate causes for creating a new state architecture, and usually, even those aren't enough.  Europe/USA has enough problems with the Islamic world without creating a new theatre for war in Europe. So the Serbs were unceremoniously squashed.  Hopefully the resulting fragmentation will soon be accommodated within the EU and allow those divisions to be reduced somewhat, but the bitterness military actions create will take generations to overcome.

notes from no w here