Milosevic is dead and gone. But the last time Serbs had control, they (under Milo) tried to set up a de facto police state in Kosovo. Kosovars were a bit resentful and naturally distrustful of continued Serbian rule. 'We promise we'll be nicer next time!' doesn't provide the best of assurances to an abused people. That's like asking a battered wife to 'stay the course' rather than simply leave the abusive relationship. Sure you can ask her, but who will seriously begrudge her if she does leave?
Now this isn't to ignore the situation of the Serb minority in Kosovo either before or after the war. But there was a right and a wrong way to approach it. And removing Kosovar autonomy and putting Serbian Milosevic cronies in every position of power while restricting the rights of 90% of the population in the country simply WAS NOT the right way.
A liberal democracy does not mean that the majority gets to beat down the minority, whether we're talking political ideology, religion, or ethnicity. The Serbian majority has a duty to its minorities. The Kosovar ethnic Albanian majority also had a duty to its Serbian minorities. Yeah, the Kosovar Albanians failed in their duty. But that doesn't excuse the Serb majority in larger Serbia from doing the same. (and more widespread and drastic as well) And when it comes down to it, ultimate responsibility lies with the highest authority. That highest authority was the Serbian government. They could have found away to convince the Kosovars to treat their Serb minorities better without beating the hell out of that Kosovar Albanian minority themselves. They chose not to.
They paid the price.