No world power will tolerate an aggressive military alliance on its borders. If you don’t understand this basic fact, then what else is there to say to you. NATO has been invading and destroyed countries for decades since USSR fell. The principle of invading countries because might makes right is already established by NATO.
It’s pretty funny that you bring up Serbia, given that what Russia is doing in Ukraine is directly modelled on what NATO did to Yugoslavia. NATO recognized independence of the separatist regions and then had them invite NATO to assist. This is precisely the formula Russia followed with DPR and LPR. Russia is just following the rules based world order here buddy.