I haven't read a lot about the Crusades specifically, but Han van der Horst discusses them in his general history of the Netherlands (Nederland – De vaderlandse geschiedenis van de prehistorie tot nu), seeing as they were an important event that affected all of Europe. What he has to say on the Crusades boils down to the following:

• The direct instigation for the Crusades came from the Byzantine emperor, who asked for military aid after the Turks had conquered some of his provinces in Asia Minor. So yes, they started out defensively. However, the crusaders quickly turned their attention to other parts of the Muslim world, far removed from the Byzantine Empire or its contested provinces – from Portugal to Egypt and Palestine.
• As a campaign to liberate the Holy Land, the Crusades were pretty much pointless. There had been succesful pilgrimages to Jerusalem before, unopposed by the local Muslim rulers. Pilgrims brought in money, after all; besides, those currents of Islam that preached tolerance towards other religions were dominant in the 11th-century Muslim world.
• Individual crusaders' motivations varied greatly. Though religious fervour definitely played a part, many knights also joined the Crusades in hopes of gaining wealth and fame, or to get out of a sticky political situation at home.

At any rate, bickering over the interpretation of 900-year-old history to support a present-day political point ('Islam is not a religion of peace,' 'so much for being the victim') seems exceedingly petty.

Not discouraging direct responses to this particular image, but there have been a few questions asking whether the Crusades were a 'defensive action' against Islam. Check these out:

• I received this article today in an email, it's essentially denouncing Islam and justifying the crusades. Can someone tell me how legitimate this is? - this seems closest to the image in question

• I saw this article about the Crusades posted on Facebook. How accurate are the bullet points?

• Given the recent uptick in Jihad versus Crusade comparisons, i've seen this image a lot, what does it ACTUALLY show? - re Bill Warner's video Jihad vs Crusades

• Were the Crusades a defensive move?

Meanwhile, check out the FAQ section Motivations for the Crusades, in particular this first post:

• Who started the Crusades? (Each one)