It seems like a funny thing for people to assume. Why should we think we are so special that in all the galaxies in the universe there is no other intelligent life out there? If life came to be on this planet, it could definitely happen on other planets. There are so many billions of stars out there. Every star could be a sun for other planets. It's totally possible that we will never find other intelligent life out there, but that definitely doesn't necessarily mean that it doesn't exist.