Not just confusing children, but literally removing the ability to be specific about sex in any written or verbal communication. The language of law, of art and culture, of online discourse, of sharing experiences, history, analysis, expectations and needs ... the ability to speak clearly about who is which sex, which sex did what to who and why, obscured away not just for the future but in records of the past as well.
And who does that hurt most?
Not men, "mankind", the "common man", the neutral "he", the default human perspective in discourse, history and culture.
It hurts women. The "invisible" half. The exception, the sex that has to be named specifically to be remembered and included, to be differentiated in data or considered in culture.