True, many are Blue Lodge Masons, 3rd Degree Masons, Skull & Bones members, Knights of Malta, etc. etc..
Most aren't, some are. Good example would be Cradle of Filth.
They are, how many people knows a friend that dress like Rihanna, has a hairstyle like Rihanna, and forbid even acts like Rihanna. I used to.
One of the oldest dualities on the world is the battle of good versus evil. Whether these symbols are used to affect people in a certain way will be just as much a conspiracy theory as the mystery behind the symbols itself. Maybe it's a matter of opinion whether a particular person believes Tomorrowland is evil of nature. Some will think it's serious, some would think it's absurd. Other would think it's meh. Personally, even if I had the chance to go to Tomorrowland I would skip it, ever since I started listening to psytrance I dropped all other electronic genres.