Problem is, if we don't judge it by our modern western standards (and even those vary), by whose standards should we judge it?
By the standards of the crusader? Then why do we judge Al Qaida by our standards? By theirs, they are every inch as justified in what they do as the Crusaders were...
My point is, while it may have been acceptable at the time, we MUST treat everyone in the same way - either judge them by OUR standards (modern ones) or theirs (which makes now sense ; they will ALWAYS be justified by their own standards), or not judge them at all.
We were asked to judge here, so #3 is not an option. #2 will get us nowhere (when it get to serious stuff, few people ever engage willingly in something they feel is unjustified), therefore we must judge by our modern standards.
And by those standards, out of all options presented, the "Barbarian assault" one is the one that's CLOSEST to how things seems. Does it absolutely mirror reality? No. The arabs were not the "utterly peaceful civilization" and the crusaders were not the "utter barbarians".
Are the other options a better representation, though?
" A shining example of Christian unity in twarting a common foe? "
Errr, yeah. Next.
"A barbarian assault on a peaceful civilisation?"
Covered above.
" A war in which both sides must be apportioned some of the blame? "
What blame is there to put on the Muslims? That they occupied Jerusalem? Be serious. This one implies both sides are roughly equally at fault, which not many here seems to believe is the case, and which history does not seem to support very well.
"Just another 11th century war? "
Which it was not, given the whole "culture shock" effect. Perhaps this answer is a more valid one, but...
Perhaps the whole matter of people picking "barbarian assault" is more of a matter of lack of choice rather than lack of knowledge.