> "You can't respond with the cliché brainwash argument either. Culture is always brainwash."
Your logic is bad.
I more-or-less agree that "culture is always brainwash." The logical follow-up is not, "Let's therefore accept all cultures that don't immediately, viscerally violate our sense of right and wrong"; it's, "Wow, culture is fundamentally really messed up! But I don't want to live in a society that eliminates it completely. How much messed-up-ness am I willing to endure to get the benefits of culture -- namely, consistency in what I'm expected to deal with every day, social stability, a sense of unity with my neighbors and countrymen, a sense of heritage, and various intangibles?"
> "I am saying we need to be careful of what we are criticising. A lot of cultural norms are always arbitrary."
So criticize all of them! The problem here is that you're working off the premise that our own cultural norms are somehow above critique, which is simply untrue.
However, I think that, even on close inspection, many of our culture's norms do more good than harm. I honestly think that most Americans would be (marginally) unhappier if it became culturally acceptable in America to walk naked in public (even if we let a generation pass so that there's no cultural shock) -- whereas I'm quite certain that at least a majority of people living in societies that force women to cover themselves and act subservient would be happier if their communities' cultural norms allowed women to act like women of first-world democracies. That's what distinguishes our cultural norms from theirs. And if any of our norms fail the shit test of "does it make life better?," for God's sake let's throw it out.