Because sometimes a pat down or body check is the only way to be sure. If you have a composite material knife that doesn't register on scanners tucked into your sock, attached to your inner thigh, or on your spine no one would know without a pat down or check. The scanner wouldn't pick it up, the dog wouldn't smell it because it would just smell like metal, and then the bad guy gets on the plane that has members of dozens of families and makes the pilot fly the son of a ***** into a building, killing even more people.
If they feel the need to search everyone to make sure that this doesn't happen, including searching me, then I'm fine with it. Oh sure, I'll be a little embarassed or uncomfortable with another guy frisking me, but you know what? I'd grow the fuck up and go on with my day, not have some kind of insecure, homophobic knee jerk reaction that some people in this thread have exhibited.