Why Christians burned people at the stake

Here is Queen Mary's reasoning as to why she thought it appropriate to burn heretics:

As the souls of heretics are hereafter to be eternally burning in hell, there can be nothing more proper than for me to imitate divine vengeance by burning them on earth.

In other words, we might as well start now what will soon be reality. I don't think you can fault her logic but somehow I can't see it persuading many today. Thoughts?