Is it? I’m going to say yes, with certain reservations.
1) The snakes should be protected.
2) Anyone handling them should be experts licensed by the state in which the church exists.
3) The church offering the activity has to have insurance that covers accidents and liability — just as fireworks displays and rodeos have to have insurance — so that if the snakes escape, or if someone is injured or killed during the service or at any time when snakes are present, they’re covered.
4) The right should be an ordinary RIGHT, and not a religious right. No special favors for churches in the possession and handling of wildlife.
Other than that … I think this is a stupid practice, and the people doing it are complete fools. But hell, let ‘em.
I’m going to suggest that if the practice is banned, or some of these nice people are prevented from “worshipping” as they wish, they go blackberry picking in East Texas. They’ll have plenty of chances to meet up with diamondback rattlers, and they can just grab up anything that slithers.