?? This makes no sense. Putting them back doesn't put the world in any more danger, if anything putting them on the moon would be way worse. If someone has the capability to "time travel" as they do in the movie, they can simply go to another alternate universe and grab the stones. The barrier isn't the existence of the stones, it's the ability to travel through the quantum realm. And how would the moon be safe??? Did you miss the part where the bad guys live in space?

And Thanos has to have an amazing fucking throw that can outspeed the lady who flies at Supersonic levels.

Sure, she should fly full speed and barrel right through the machine she's trying to use.