Luther didnt start it
It was smoldering until he lit the fuse.
To deny his thesis is the point of eruption is just plain ignorance.
It had many things that were in place, but his letter was the straw that broke the camels proverbial back.
For lack of other points, all historians agree his these is what did it. No going back after that.
I wrote a college these on this. If you are ever interested in reading not. I did post it to FR years ago.
My thesis is that the Renaissance is what actually set it in motion, and we could make an argument that the Black Death had a huge part in it.