Classes can be destroyed and we can build class-less societies without hierarchy in lieu of anarchism.

The whole point of socialism is transitioning to that stage. To get there you need to supress the reactionary classes (bourgeoisie) just like how for them to stay in power they suppress the proletariat. Then they can with time be expropriated and proletarianised until their is only one class the proletariat and class antagonisms cease to be. Pressing the magic communism worldwide class destruction 9000 button isn't an option no matter how much you wish for it.