Yeah, funny what people will do to avoid being killed.
You'd better study up on your history. The death penalty for heresy was unknown until the 12th Century, 700 years after Jerome. Oddly enough, the man who came up with the idea was a heretic, the Emperor Frederick Barbarossa.
The arch-heretics of the first millenium weren't killed. Arius wasn't killed. Nestorius wasn't killed. Pelagius wasn't killed. They were removed from their offices and their writings were burned.