From a religious standpoint the Crusades were one of the worst evils that ever came to pass. Outreach to that part of the world has ever since used this period as proof against us.
Islam might extend their empires by force, but the civil sword can never spread our faith.
Politically, however, the Crusades would have been a just war (even if fought unjustly).
I say WOULD HAVE BEEN instead of WAS.
It would have been just if the objective was to defend their lands from Islam.
But the objective was, largely, to take over the Holy City (Jerusalem) in preparation for a millenial kingdom. Therefore, even the motive was wrong.
Also, the evil objective of most men was either/or or a combo of (1) getting sins forgiving by an action, or (2) getting some loot!