Matthew grew furious after Jeremiah accused him of burning slaves in the church, while it wasn't necessarily an accusation for it was the truth. They did turn some slaves to vampires and had to burn some inorder to fake their own execution.
During that time the knowledge of vampires and night creatures was overwhelming. Secret societies were formed to try to find a solution, and Matthew alongside his brothers didn't know that they were immortal hence they were afraid of death. The sun wasn't the case since they could walk in it hence that alone caused less suspicious and humans trusted them.
But those who couldn't walk on the sun were the ones who were burned in front of people to witness - and the rumors would dissapear. They did that for over two hundred years sacrificing vampires they turned for the sake of protecting themselves.
