Which subethnicity started it or whatever doesn't fucking matter., this whole line of thinking only leads to more hatred, more destruction, more dysfunction.
As a Croat, my enemy is not my fellow Yugoslav, my enemy is the nationalist thugs on all sides that destroyed my country so they could rule over their hateful little fiefdoms.
Bratstvo i jedinstvo is coming back, under a blue flag with yellow stars. Montenegro is joining the EU next, with Schengen etc bratstvo i jedinstvo between crna gora and hrvatska will be restored.
It's more accurate to say "whoever had the upper hand at a given time" was using their temporary advantage to terrorize the others over the last couple centuries.
Given this, it's easy to understand why Serbs wouldn't want their friends and families living in states administered by people who were massacring them with the backing of Nazis and/or Ottomans within a generation.
It doesn't justify the atrocities of the Milosevic era, and it's still technically correct that "yes, the Serbs were the lone bad guys" but only if you choose to look at a certain decade and pretend history doesn't exist before that: which is very much how the American news media at the time "sold it" to justify U.S. involvement in the region.