Aristotle was against testing ideas. he came up with an idea and then spread it as truth without ever checking. He spread this view to others which is pretty much totally against the scientific method. He made several claims that were just plain wrong, but no one called him on because he was Aristotle.
He claimed that Nature abhorred a vacuum, thus one couldn't exist. He claimed that heavier objects fall faster than light ones. He claimed that infinity and the void (zero) didn't exist, which kept us locked into Roman numerals long after the rest of the world moved on to a more modern system of counting and mathematics. He even claimed that Men have more teeth then women.
The fact that he was Aristotle lead many to accept everything he said as fact and not to think about it anymore, Think about what Rome, or even Greece could have accomplished if they weren't saddled by all of his false assumptions. In the 350 years since Newton rejected Aristotle's view on the universe and replaced it with one based on observation and experimentation, we have gone to the moon and back. If this attitude was adopted during his lifetime where would we be today?
it's been a while since I read that book, and I highly recommend it, it's an amazing story that is very well told, so I don't remember things detail for detail, but it's clear that those that followed Aristotle did not once think to question his pronouncements, and it held everyone back. It might very well be his followers and students that were the idiot, but it was his legacy that held us back for so long.