I have a some extracts of the chronicler Ibn Al-Athir (1160-1233) about the First Crusade and, re-reading them in light of your question, it's actually quite surprising how factual he is in tone and how little he engages in demonizing the Franks, as Muslims called the Crusaders. Certainly Ibn Al-Athir regards the Muslim rulers whose cities were conquered as having been just and equitable men who tried to protect all their citizens (Muslim, Christian, and Jewish), whereas he describes the Franks as achieving some of their conquests via treachery rather than military superiority. He does describe the slaughter of countless Muslims at the hands of the Franks, but the letters and chronicles of the crusaders report exactly the same thing. Ibn Al-Athir interestingly suggests that possibly there was some kind of secret deal made between the Fatimid caliphate in Egypt and the Franks, because the Fatimids felt threatened by the Seljuks who had comparatively recently taken a lot of formerly Fatimid territory in Syria, Gaza, etc. He is careful to state that this is just a rumor, of course. Ibn Al-Athir did believe, however, that the success of the First Crusade was largely the result of the dissension among various rulers of the Muslim world, an assessment with which the modern historical literature I've read agrees.

It probably would help for you to clarify your question a little, though. I mean, when has any nation or people felt that an attack upon them was justified? The Seljuks did not in fact commit the rumored atrocities in Jerusalem that were being reported back in Europe and that provided the pretext for the Crusade. It was more difficult under their early rule for pilgrims to reach Jerusalem, but that likely has as much to do with the unsettled political situation as anything else. The Seljuks did, over the course of the eleventh century, conquer some territory at the eastern fringe of the Byzantine Empire, and probably would have thought that if they were going to be attacked by Christian troops, it would be there, and by Byzantine armies. The sheer improbability of a European army marching all the way through Asia Minor only to push on to Jerusalem also played a role in the success of the First Crusade.

I'm not a specialist in this topic, though, so hopefully others will contribute also.