Americans of Iranian ancestry fear they will be blocked from visiting Europe in "retaliation" for the discriminatory US policy.

For other countries to "retaliate" by restricting US citizens of Iranian origin (and Iraqi, Syrian or Sudanese) would be ridiculous, like "retaliating" against Nazi Germany by punishing German Jews. A meaningful retaliation should infuriate those responsible for the US policy. That's why I suggest imposing a visa requirement on US citizens whose family names start with "Ry".