"Garand Thumb" is real. I've seen it. It's also like lowering a hammer on a hot chamber. It can be done safely if done correctly. I've handled and fired a lot of Garands over the years, and my thumbs are fine.
When loading the clip or depressing the follower to let the bolt go home, place the back edge of your little finger into the curvature of the charge handle and keep it there while using your thumb. Depress/load until the bolt is released...and roll your hand forward and up. If your pinky is short, use the ring finger. Simple as that.
Most Garands that I've handled don't release the bolt suddenly when seating a clip. The majority of them won't go home at all until the charge handle is helped along after the clip seats.
If your front porch collapses and kills more than three dogs...You just might be a redneck