All countries on the list are failed states

All countries included in the temporary immigration ban are either failed or deteriorating states (Syria, Iraq, Libya, Somalia, Sudan, and Yemen) or are actively hostile to the US (Iran).

The Muslim-majority countries NOT on the list (Saudi Arabia, Kuwait, Lebanon, Jordan, Egypt, Afghanistan, Pakistan, and Indonesia to name a few) have stable (for now; crossed fingers) governments in place. Some of them are pretty shitty governments, mind you, but still relatively stable.

Based on this premise alone, there shouldn't be anything legally wrong with this temporary ban.