This was one of those difficult decisions that political leaders are paid to make. From where they sat, and from where we sit now, it was not the wrong decision to make. It was more like Churchill and FDR arming and supporting Stalin to get rid of Hitler, than like Churchill and Lloyd George promoting Japanese expansionism, Leninism, Zionism, or Saudi Wahhabism in order to disloge the Kaiser and the Ottoman Empire -- a justifiable choice of one demon to defeat a more pressing one, rather than something unprecedented or unjustified. Indeed, FDR had embraced a great known evil, in a way that Carter and Brzezinski did not. We'd had good relations with the likewise "Fundamentalist" Saudis for a long time, so the dangers at the time would have appeared to be much less than they do in hindsight. Ought they to have known? They might have known or guessed at something, but there is no way they could have known what we know now. If things go horribly wrong now, we may regret their decision, but I think it will stand as the right decision for the time and the right decision overall.
Zbig has the arrogance and vanity one expects from intellectuals in politics. He sounds insufferable, but at least he does stand by his decisions, rather than try to palm them off on the other party if they become unpopular. And that is to his credit. There is more continuity in our policies than parties and ideologues will admit.
The other thing about these remarks is that politicians improvise. They do what they can at the time and hope for the best. Indeed, they hope that others who come later will make everything right. The critical period was not in the Carter or Reagan years, but during Bush I and Clinton.
My mistake, it wasn't the British who supported Lenin, but the Germans. They also tried to get Mexico on their side by promising them Texas and the Southwest. To be sure both the Germans and the meddling British of the same years thought they were struggling for their lives, but the evils they unleashed were greater than those they were fighting against. I don't think Carter and Brzezinski are in their category.