The Passion of the Christ

For those of you who have been living under a rock for the last month (and for some reason came to this site first), Mel Gibson's movie comes out this week.

Some of the hubub has been over the selling of pendants in the shape of nails. I'm a little at a loss as to why people are pissed about this. I hear the "profiting off of Christ" argument, it just doesn't make sense. How is a nail different from a cross or a crucifix? Or have the people pissed off always been against that too, but had given up until this brought the issue up again?