Why? Words can have more than one meaning.
Edit: looking at all of the damage this has spawned, I'm sorry. Blame me. I didn't think everyone was going to get taken out from this.
And others disagree with this, and consider your efforts unnecessary. I don't think the two camps will ever agree, mostly because it's very hard to prove that using "man" as a synonym for "humanity" implies that women aren't a part of humanity.