Religion and the State
Whenever religious leaders get political power, they try to use the power of the State to enforce their religious beliefs on others "for their own good." This applies to most religions. I do not know enough to say there aren't exceptions, but I doubt it. Freedom of thought entitles people to speculate about the Big Questions: Why are we here? What was there before the Big Bang? What happens when I die? Is there an Intelligent Designer behind the Order in the universe? The most common problem with religion is fundamentalism, when someone claims to have the Final Answers written down in a book, and persecutes anyone who believe something different for being heretics. This is part of the bigger problem: when a religion, philosophy, party enforces its theories at the point of a gun. Otherwise, religious speculation can be an entertaining pastime for our spare moments.