His condescension does come from male privilege, but it still doesn't make "mansplaining" an acceptable term.
Mansplaining *means* 'condescension that stems directly from male privilege'. If that is what is happening, and mansplaining is the accurate term for it, I fail to see the problem.
It allows someone to dismiss someone's arguments based on their gender and not the content of their arguments. I don't dismiss your statements based on your gender, please do me (and other males) the same courtesy, even if our statements are totally moronic. Dismiss them because they're moronic.
No, it allows someone to dismiss their arguments because they are condescension that stems directly from male privilege. It does not dismiss the arguments because they come from a male. Not all males speak with condescension that stems directly from male privilege.
To be crystal clear, dismissing 'mansplaining' IS dismissing statements for being moronic, not dismissing them for coming from a man. It's a particular subset of moronic.
I'm not objecting to your characterization of his statements, I'm objecting to your using a sexist term to dismiss him. Again, you wouldn't want your statements characterized with "that's her PMS talking," so why is acceptable to say, in effect, "that's his Y chromosome talking"? It's very hard to listen to someone when they're doing something while complaining that another person is doing it. If you want to call him sexist (and I would strongly agree with you), don't use a sexist term to do so. It does nothing to advance the discussion.
I don't know why you think these are equivalent. "That's her PMS talking" is actually bypassing the argument. Characterizing an **argument** as 'mansplaining' is not at all bypassing the argument, it is addressing the content of the argument head on.
There's a massive difference between saying 'ignore him, he's a man' and 'ignore him, his argument sounds like condescension stemming directly from male privilege'. The second one is not an inherently sexist statement, by any stretch. And it means the exact same thing as 'ignore him, he's mansplaining'.