Here, the crusaders conquer Egypt, either during the reign of Amalric I of Jersualem, or during the 5th crusade. The question is how this affects the kingdoms south of Egypt. Are they pressured to convert to Roman Catholicism? Are they invited to assist in the government of Egypt? If relations with Nubia and possibly Ethiopia develop, would earlier contact with Africa possibly affect European attitudes towards the African slave trade and race?
The population of Egypt is way too large for a Crusader state to make much impact on it. If Napoleon couldn't manage to hold it, I doubt a bunch of Medieval knights are going to do much better.
An ephemeral presence in Egypt is not going to change anything about attitues toward race and slavery; for that you need the Enlightenment, the Scientific Revolution, and about 1,000 more years of intellectual development in that direction.
If anything, having access to Egypt's slave markets is likely to make Europeans connosieurs, as the best quality slaves could be found there.
What might happen, though, is that you might see the Levantine community in Egypt increased in size and prominence as it was in the Ottoman Empire due to the Fourth Crusade. You will also probably see much different political development in the region, as the overthrow of Egypt's government by foreigners is likely to see it replaced by something different.
Giovanni Giustiani of Siege of Constantinople fame, wasn't actually Genovese, he was a Levantine of Genevese descent - his family had been in the Middle East for centuries.
Anyway, this would probably increase France's prominence in the East Med.