I shoot lefty, and in competition too. There are no issues. I've never seen a garand drive brass straight back (which would be an issue) if it does, it's a malfunction that should be addressed.
M1carbine, on the other hand, is a different story. I have an NPM that I can shoot lefty just fine, and an Underwood that pops me square in the forehead every shot, unless I shoot it right handed.