Crusades have nothing to do with the Renaissance. Neither does the jousting and the heavy weapons displays/booths/games that so often populate a RenFair.
They really shouldn't even call the things "Renaissance Fairs." There's no appreciation of rising literacy, growth in secular art, explosion of scientific knowledge, increase in religious freedom of expression, or any of the other elements of the Renaissance.
All everyone cares about is knights, armor, swords and hawt chicks. And mead and turkey legs. Which is totally cool in its own way.
I was just put off by my first time attending a RenFair and seeing nothing pertaining to the, you know, Renaissance.