The archaeological sites on Easter Island are fragile and easily damaged by thoughtless actions, such as climbing on the fallen statues or walking on petroglyphs. The volcanic tuff is soft and easily broken off or scuffed. Incredibly, some people have scraped ancient rock carvings with stones to make them easier to photograph!
Cruise ships can unload hundreds of people a day, and the large groups often spin out of control, swarming over the quarry at Rano Raraku or standing on the stone house tops at Orongo (several of which have collapsed in recent years).
The national park has had to erect stone walls around many sites to keep out rental vehicles and local residents have organized voluntary projects to pick up trash discarded by tourists.
Though it may seem that these places are remote from the world of high-impact consumer tourism, they are in fact endangered by the selfishness of some visitors and those locals who would profit from them.
It's strictly prohibited to remove any ancient artifacts (such as spear heads, fishhooks, or basalt chisels) from the island. The warning signs erected in the park are there for a reason, and the human bones occasionally encountered on the ahu and in the caves deserve to be left in peace.