Answer:
It totally depends on your perspective, your history, and how you WANT to look at things. Both sides of the coin can have strong arguments.
Step-by-step explanation:
In this case, I will argue that the Crusades were justifiable not only before, during, but also after. But before we can argue whether the Crusades were justifiable, we must first define the key term(s):
1. Justifiable: Having, done, (something) by a good or legitimate (key word) reason.
Already, we have a term that gives us two sides of the coin. Both sides of the coin can be argued in a positive sense.
1) The Crusades have a legitimate reason: The Crusades was started by the Catholic Church under the legitimate reasons that the "Holy Promise Land" was under attack by the ever growing presence of Muslims & Islam. In order to protect Christian sites (the reason), the Crusades were created to reopen access and try to keep those access to the holy sites.
2) The Crusades was one of the first globalization movements following the fall of the Roman Empire: The Crusades helped unify many opposing European States (for example, France & Great Britain, Spain & Great Britain, etc. etc.) to fight & work together for a common cause (defeating the Muslims). This led to a brotherhood and a more positive relationship between two (or more) entities or parties. On top of that, the European countries had some of their first enlightenments (from the Dark Ages), as medicine, technology, ideas & beliefs, traveled back and forth from the Middle East & onwards to Europe.
3) The Crusades led to advancement in European society. This statement essentially piggy-back off of the globalization point, as technology, methods, and even resources were able to change and influence European lives, mostly for the better.
4) During the Crusades, Europeans were able to interact on a greater scale with those outside their beliefs, i.e. Jews who lived in the land, Christians who had stayed over the years, and even Muslims who were under their reign. This deeply influenced the way Crusaders ruled as well as how they acted while as a ruling party (rather than as the invading force).
However, we can note that the crusades were not all bright for not only the Middle East but also Europe:
1) Display of disappropriate amount of power by the Catholic Church: The Catholic Church, while seen in a positive light in being able to unify the European Nations & People group during the Dark Ages, reered it's ugly head in trying to create a more "godly" environment. In essence, the Church took advantage of the Christian community, and by limiting the people's access to the Holy Bible (the ruling book the Catholic Church said it was based off of), the Catholic Church could then give decrees that are stated to be "from GOD", but may not be. This can be seen in the Crusades, in which the Catholic Church called each Crusades a mandate from God even though it was not.
2) The Crusades started a large amount of unrest that continued throughout the years even to today: Traces of civil unrest can be seen even today (though not as major as before). Take for example, the creation of Israel. While the state of Israel was largely based off of the ancient texts and history, Arab & Palestinians base their claims off of the overall victory during the Crusading days. In the argument that the crusades were justified or not, we can essentially see that if they weren't, and they were stopped after the First Crusade, the conflict of today would not be occurring as often.
3) The reason itself soon was lost after the first two crusades, and were essentially a tradition afterwards. Justification was lost later on, and only became a journey to prove a Christian's worth. By no means was the later Crusades justifiable, though they were by name.
In the end, the opinion is based on one's own opinion. However, it is safe to say that the crusades were justifiable, but only to a certain extent. Look back to the definition of the crusades. The crusades were based off of a legitimate reason, but were they a good reason in the following ones? While the Church may deem them so, History would show that they weren't. So to answer the question, the Crusades were only justifiable up to a certain point, and definitely depends on the viewpoint of the observer.