The law's the law. Not only did they break it but they broke it with the intention of being arrested then resisted arrest so they could make the cops look bad and whinge about alleged infringements of their liberties. The right to peaceful assembly is not a ticket to be an arsehole. You can't hold a peaceful assembly inside a fire station, in an ER room, inside a nuclear facility or any other number of places that have restrictions on public access. This is not a breach of peoples' rights it's common sense.
Someone made the decision that those who enter the Jefferson memorial have to maintain a reverential atmosphere. Whether you agree with this decision or not is neither here nor there. It's law, it's not a breach of anything and cops will rightly arrest you if you break that law.