Leading US generals are extremely angry at the conman for abandoning the Kurds. Those who have retired are saying so.

The argument that the US should not abandon an ally has validity, but only to a certain extent. It was used to argue for continuing the war in Vietnam, and the war in Cambodia. ISTR it was also used in Iraq, and I think it has been used to argue for continuing the war in Afghanistan.

In the case of the Syrian Kurds, this argument reinforces other reasons why the US should have defended them.