Leaving aside the numerous ways radical political change can be achieved for a second... communism is incompatible with human nature? You mean, the classless and stateless arrangement that characterized the vast majority of human history? Not to sugar-coat "primitive communism", which certainly had plenty of ills that stood to be cured, but you couldn't be further from the mark. States—feudal and then merchant-capitalist and then capitalist—have continually been imposed. There's a reason that all of these "advancements" have been resisted everywhere they're evangelized at the end of a weapon.
Now, could communism be achieved without force and mass murder? (It's best to note that force is not necessarily the same thing as mass murder.) Certainly, why not? Scarcely any of the blood shed carving out the social democratic features of the primarily wealthy countries has been on the hands of the people seeking those features. There's no reason to believe the same course can't be followed indefinitely. While this course has certainly suffered setbacks, the overwhelming majority of people favor it. It's only the vast accumulation of power in the hands of a tiny elite that is holding it back, and now the only real weapon available to them is the erosion of democracy (now who's engaged in force?).
Be that as it may, most of the history of radical change is characterized by violence. If communism were to be achieved by force, the worst other revolutions could claim is that it failed to rise above their own moral character specifically in terms of means.
I don't want you to take this to mean that I think a violent communist revolution is desirable or even excusable (I'm not even exactly an advocate of communism, full disclosure). But for fuck's sake, let's at least be honest—about human history, about "human nature", and about the long storied history of political upheaval.