An EVA is dangerous business for a number of different reasons. The primary one is collision with debris. Orbital velocity at 300km above the Earth (typical for a Space Shuttle mission) is 7.7km/sec. A particle as small as a fleck of paint or a grain of sand has the kinetic energy of a rifle bullet! Every space mission creates more orbiting debris, so this problem will continue to become worse.
Scientists are developing tele-operated robots for outside construction work, to eliminate the need for EVAs. However, the first of these systems won't be ready until at least 2003.