That is not necessarily true. Some iguanas make very good pets. The males can be more aggressive than the females. It depends on how the iguana is raised, treated and socialized ... just like with any animal.

We had a six foot long male iguana. He was not aggressive at all. He took naps with me on the couch, and had free run of our living room.

Iguanas make very good pets, for someone who takes the time to do the research into proper care, treatment and socialization.
Not everyone can or should own one, but not everyone should own any pet.