The excuse is the same or similar one to why guns are banned on school Grounds. Because a large group congregates and there are children present. The difference is that Public Schools are Government property and Churches are not. The Government CAN regulate Government property.
A number of Southern states also ban snake handling in churches:
...Many state legislatures have long maintained that religious freedom does not extend to picking up venomous snakes.
In the decade between 1940 and 1950 six Southern states - Kentucky in 1940, Georgia in 1941, Tennessee in 1947, Virginia in 1947, North Carolina in 1949, and Alabama in 1950 - banned the practice of snake handling. In each instance,
state lawmakers based their legislation on the premise that the First Amendment right to the free practice of religion was superseded by the potential danger to non-participants.
In Alabama and Georgia the practice was ruled to be a felony while the other four states deemed it a misdemeanor. The logic for a felony charge was that if someone violated the law and a death occurred, capital punishment was a reasonable sentence. However, Alabama and Georgia later repealed their laws....
Snakebite kills preacher: Should snake handlers be subject to prosecution?