Would someone mind explaining to this Arab immigrant (since I think I need to state my racial and ethnic background to get answers) why it's seen as acceptable to make broad generalizations based on race and sex in this way?

For what it's worth I'm sitting with two of my asian friends, who agreed with the quoted sentiment, so it's definitely not just "middle-to-upper-class white males" who hold these views.

I also know I'd think very little of someone who tried to dismiss a viewpoint of mine with something that amounted to "of course you'd think that, you're Arab*