It took a LOT of work (about a year's worth) but I finally got my neighbor (who is also a coworker) to stop killing the snakes on his property simply by continuing to share my enthusiasm for all things reptile and showing him pics of my eggs and baby snakes. The more I taught him about snakes and how to identify the ones in his yard the more interested he became. He *just* came to me last week and announced that I would be proud of him because he let a snake live on his property to which I told him that I was not just proud but over joyed. Most of what was motivating him to kill snake was fear of the unknown.
...but changing the views of everyone in Texas....that's a harder task.