Hand tools are useful in building a wall. Of course people have built some pretty amazing walls without the use of even tools such as hammers and chisels. But a hammer definitely helps. It is an extension of the fist which is pretty useless when it comes to breaking rocks. And a chisel I suppose is like an extension of the fingernails. They (fingernails) are good at splitting and prying open things and scratching lumps off things, but not rocks.
So hands that are thinking wisely about laying stone efficiently choose hand tools to make their life easier. I didnt say less dangerous. As soon as you introduce the simplest of hand tools you introduce an element of danger. It will be more easy to get the job done but more easy to get hurt too . The trade off for efficiency has always been thus.
If I walk to work, I get there slower. If I bicycle there, I will likely get there faster but I risk falling off and breaking my arm. If I drive, it gets me there even faster but I increase the severity of the consequences if I drive badly, or someone else does.
Hands can get hurt all the time if they are not thinking. Usually it is from a rock rolling or dropping onto to a finger or a thumb. But hands usually take more of a beating from each other. My right hand has smashed the daylights out of my left hand many times. I've got chips of stone in them and splinters of handles and scratches and grazes from all sorts of configurations of using my tools.
It seems funny to think hands can inflict so much pain on each other. But if the hands are thinking at all, they try to minimize these confrontations and unlike stonemasons they almost always 'make up' right away if one of them hurts the other.
