Were the Crusades justified? Strange question. When one considers that each crusade was so different, it's nearly impossible to answer. I'd say that the First Crusade, and only the 1st was justified, and that is just the war with the Muslims, and not the monstrous attacks on the Jews and major Church figures in Germany at the same period. That was a total disgrace. The only redeeming part of that is that many Bishops in Germany spoke out against the attacks on the Jews, and even protected them personally. I remember that one German Bishop was murdered by anti-Jewish "crusaders" when he protected a Jewish family.
And yet the 1st Crusade in itself was justified. The Church took it (understandably) hard when Islamic armies took over the Holy Land, destroyed the Church of the Holy Sepulchre, and taxed the Christian and Jew communities to death. The Muslims had for years been raiding the European coastline, destroying abbeys, as the Vikings were doing in the same period, and the Irish had done in the Dark Ages. The Islamic Empires were not only trying to take back Spain at the time, but they were approaching the Byzantine Empire's capital, Constantinopol, and about 10 years before Pope Urban II launched the 1st Crusade, the Emperor of Byzantium was captured by Sejuks and his army destroyed at the Battle of Manzikert. Ever since then, the new emperor, Alexius Comnenus, feared an attack, and thus sent the Pope a plea to come to his assistance. The Europeans, the Christian ones anyway, did see Byzantium as necessary, as when it fell, the Christians of the East were put in very serious danger indeed. Of course, by the time the crusaders were finally at Constantinopol, Alexius had gotten over his fears, and promptly slammed the doors on the crusaders, who promptly opened them up again. Though the Crusaders were very brutal in their attacks, they got the job done. I'd say yes, there were many reasons as to why the First Crusades were justified.
The Second Crusade was also somewhat justified. The Kurdish armies around had taken Edessa and were moving in on Antioch, and so to protect the Holy Land and the Byzantines once more, they launched a crusade more brutal and terrible than the first, and lost it. The 3rd Crusade was simply a continuation of the 2nd, and it took back little land. The truly unjustifiable crusade was Venice's 4th Crusade, which was not really one supported by the Church, and was instead ordered by the blind Doge of Venice, Henricus Dondalo. It was announced at a masquerade ball, and I have the impression that everyone was a bit tipsy that evening, and the Doge popped in, with a Crusader's cross on his skull-cap, ordering a new crusade. Of course, they never got past Constantinopol, which they entered, and sacked, looting most of the Orthodox Churches (including the great Hagia Sophia) there, and generally acting as horrendous as possible. Actually, as soon as they returned to Venice with all the loot (which they decorated the City with) the Pope excommunicated every one of them, including the horrified Dondalo himself.
your Holiness!