What does this all mean? Let me break it down for you, real easy like. Bowser, King of the Koopas and all evil, is a mean, animalistic, sadist/dom character who wears aggressive fetish wear. His army is spearheaded by shock troops that are all phallic in nature. These troops march into the Mushroom Kingdom, attacking gender-neutral toads left and right, enslaving them and oppressing their idyllic ways. These asexual toads are ruled by the hypersexualized Princess Peach, a symbol of all that is feminine, once virginal but now sexually aware and powerful, in a commanding female way.
Given this clash between feminine sexual dominance and bestial male brutality, is it no wonder that the Mushroom Kingdom is populated by sexless denizens? Is it no wonder that Birdo and Yoshi, the two characters who are removed from this clash of gender due to them transcending it, are paired together? Can we really be surprised that Mario, hero of the realm, a figure of general masculinity, wears a male fertility suit that has been effectively castrated and feminized? Of course not. To side with the Mushroom Kingdom is to side with the female. To side with the Koopa King is to side with inherent male-ness.
And that is the true source of the everlasting conflict that drives the Mario universe.