Most serpent handlers that I have known were honest and sincere believers who gave
Mark 16:18 as much weight as the 17th verse. If one verse said believers would speak "with new tongues", then the other verse- that they would "take up serpents" must also be true. They literally take God at His Word. To the extreme, to be sure, but the fact remains, they believe what the Bible says. Some even believe the word "shall" is a command... that the handling of serpents is a direct command of God.
I have known "believers" who handle serpents (attended 2 services...one where it all began in a place called "Dolly Pond", just north of Chattanooga), to drink poison and to handle fire. Never saw the last two, but know people who claimed to have done them.
God, in his infinite wisdom, I believe, gives us Scriptural precedence to help us to keep from going to the extreme in these matters. One, in
2 Kings 4, when people accidentally ate poisonous food. And in Pauls example when a viper bit him.
I was in a serpent handling service in Georgia and noticed the "handler" placed the box container a rattler on an Air Conditioner vent and left it there for quite awhile. At just the right time, when the "annointing" came on him (i.e., when the cold-blooded reptile was lethargic and almost lifeless from the cold air), he took it out and "proved his fake...I mean faith". When the snake began to warm up and began to move, he put it back.
Those who practice serpent handling, for the most part, are earnest in their faith. I neither condemn nor condone their actions. Nor will I participate. I fully believe God protects us from harm...but I also know God gave me enough sense to not play with fire. Or snakes. Or poison.