For many it's the sunk cost fallacy.

They've rhetorically, unreservedly supported Israel for half a century, and they will not be reexamining those intransigent beliefs today, thank you very much.

"The Doctor: How much blood will spill until everybody does what they're always going to have to do from the very beginning -- sit down and talk! Listen to me, listen. I just -- I just want you to think. Do you know what thinking is? It's just a fancy word for changing your mind.

Bonnie: I will not change my mind.

The Doctor: Then you will die stupid."

-Steven Moffat, excerpt from Doctor Who