Language is powerful. Language not only expresses our thoughts, it shapes them. “Balls” is in common use, and that’s precisely part of the problem. It’s embedded so much in our language that we don’t notice it, but that simply means our sexism is burrowed in deep.
Am I exaggerating the effects of using “balls” and similar gender-specific slang? I don’t think so. Quick: what do you call someone who has no balls, who is a weak-willed individual? Why, a “pussy” of course.