Loading a Garand properly or closing the bolt without maiming yourself just takes a little practice.
Marines and GI’s did it millions of times in WWII and Korea.
I loaded and fired mine left handed in boot at P.I. and still do.
Never had a problem.
A properly timed Garand involves four main parts. Bullet guide, Follower Arm, Follower Rod, and Operating Rod Catch. To correct bad timing (using a timing block) involves replacement of these parts and combinations until the sequence is correct.
An untimed Garand can tend to want to close the bolt early which results in the “Garand thumb” in question.
If you go back and look at early John Garand films of him demonstrating his weapon, there was no problem with the thumb.
I fired it a few hundred times, only had a problem 4 or 5 times. That was too much for my taste. Every time I slip up, it's way too memorable. The M1 Garand is the only firearm I ever owned and got rid of.