But that's all post-9/11 reasoning.
No it's not. Frankly anyone who didn't think the United States would invade and destroy the government of Afghanistan over 9/11 was a moron.
More to the point, you didn't read the bit about the history of terrorism and the value of grand gesture vs. constant pressure.
None of this is morally relevant. Morally right and strategically right are two different things.
Reread the last line. To them, tactical failing on this magnitude
is moral failing. When your cause is taken up solely because it is just, because it is the only correct, moral course of action, what is it when you set it back? Injuring good is, pretty much by definition, evil. (To say nothing of the personal loyalties this action would ultimately betray even in the attempt to serve them.)
It's absolutely morally relevant if you advance the cause of evil and harm the cause of good.