If it's true, as OY alleges, that they refused to belt up when told to, the crew were legally and operationally entitled (and right) to disembark them.
Passengers have to abandon cultural tendencies if they happen to break the law or clash with reasonable airline safety SOPs. If they elect not to do the latter, they forfeit their right to be passengers. They can go back landside and be as culturally true to their heritage as they like.
The fact that they also happened to be Arabs would not work in their favour at a time like this, and I feel sad that the world should have gone this way, but it has done.
Any sign of the Muslim faith is now also, sadly, a disadvantage to those Muslims who wish to fly peacefully.
Right now, if a man even of white caucasian appearance was on my flight and got out his prayer mat at sunset and began bowing Mecca-wards in the aisle, despite my natural liberalism my new-found paranoia would start to win. I'd be watching the guy for the rest of the flight, wondering if he was preparing for the imminent Seventy Virgins instead of leaving the time of his death, as normal Muslims do, to the will of Allah.