It is not all Muslim Visa holders, but from 7 countries that were determined by the Obama Administration to be a security risk to the US because they don't do adequate screening at their airports. For example, Turks can come to the US as can Muslims from Israel or anywhere else except those 7 countries.

The Visa issue is regrettable, but it is only temporary and the people will eventually be able to return. Those in the US can remain here and not asked to leave as in the case of BrExit.