It is primarily a British patriotic celebration (commemorating the foiling of the Gunpowder Plot in 1605) but it has a long history of anti-Catholic elements. It was for this reason George Washington forbade his troops to celebrate it.
Even to this day in parts of England, anti-Catholic aspects of the day continue, though with the loss of religion there in general, it's taken on a mostly secular tone. Like many other things, just an excuse for people to get stoned and rowdy.
Riot police with LGBT flag colored water pistols and nerf bats responded. I can just hear a police commander with a bad lisp yelling harshly into a bullhorn.
Here in the colonies we called it Pope’s Day. There were Teo separate gangs in Boston. Each had a parade with
an effigy of the Pope. When the two parades met, they would fight each other. The winner was the one who captured the opposing Pope.
The Gunpowder Plot was an attempt by a group of Catholic English men to blow up Parliement. It WAS about religion.
The anti-Catholic Part is understandable under the circumstances.