At this period in 1812, as in the Revolution, the military thinking was that actually shooting at an enemy to Kill him specifically was considered as Murder. Prior to actually pulling the trigger the soldiers would actually close their eyes, or look away from their sight, when they pulled the trigger. Therefore if they did hit someone it was considered an "Act of God". Which it pretty much was.
By the time of the Civil War the accuracy/reloading time problem had been solved for the standard rifle muskets of the time. However, the most accurate rifles, as the Whitworth and Kerr, were still as slow to reload as ever because of the rifleing systems that gave them that accuracy. So the actual snipers that used these rifles still had to be protected, and did not usually opperate in front of their respective armys positions, less should their positions be found out they were easily outmanuvered and eliminated.