most Arabs are already prevented from entering the US
Fixed that for you. Not all Arabs are Muslims, as not all Muslims are Arabs. At the same time, all they need to do is undergo a little bit of additional screening and get a redress number. It's not that bad.
For what it's worth, I voluntarily accepted additional pre-screening and am now a member of Global Entry and TSA Pre, and it only makes my life easier. It saves a lot of time when entering the US, or passing airport security. It saves the CBP and TSA a lot of time, knowing that I'm a low threat to security. And the information I had to give up was no more or less than what I already provide on a international flight to the U.S. anyway. Oh, except the fingerprints, but they government already had them (which is also true for most Arabs, as they at least once applied for a U.S. visa).
In fact, if the U.S. embassy would just add a little option to the visa application that said:
[ ] Send all information to the TSA and CBP for expedited services.
A lot of problems would have been solved. DHS handles visas anyway, and CBP and TSA are both subdivisions.