Alice - you are so right. It seems bizarre that the same people who will call out other forms of oppression at 100 paces seem to be oblivious to the very same tactics and mechanisms of oppression in a gender context. In fact, they will even trot out the same justifications for sexism that they would blast if suggested by someone else in the contest of say heterosexism or class bias.
I have a little theory that perhaps the political is a little too personal for many left of centre men (and women.) It's relatively easy to call out injustice when you can put lots of fresh air between yourself and whoever it is you see doing the oppression. But, they eschew the idea that they themselves could be at the very least colluding with if not actively perpetuating oppression of women because well, they often share their lives with them.
So, they will go through all sorts of contortions to either a.) minimise the impact of gender oppression on women, to show it's not that big a deal, it doesn't effect all women, it's not done by "good men" like them, or that popular line now, that women make different "choices" so it's not really oppression, or b.) flatly deny that gender oppression exists, often drawing on the most far out logic, dodgy evidence and anecdotes to prove that it's a figment of women's imaginations.
Oh, and there's the old, "what about the menz?" curveball they sometimes through, which is a bit minimising (well, it affects men, too, so that negates whatever impact there is on women,) and a bit denial (well, it's actually worse for men, so no big deal for women.)