Why do mormons think they are perfect people and everyone else is no good and going to hell? Wasn't Joseph Smith a false prophet?

Huh, yeah, I wonder why they never thought of that. Maybe we should inform them.

We don't think that. We have a ton of flaws, just like everyone else, and only Jesus can save us. Our goal is to help everyone come unto Jesus Christ. I worship God according to my conscience and hope that you will do the same. I believe that Joseph Smith was a true prophet, like Moses or Peter, but that is something that everyone has to figure out for themselves. A good place to start is by reading the Book of Mormon and asking God if it is true.

comeuntochrist.org

Joseph wanted to bring back 1st century Christianity . But the Utah Mormons ruined his reputation by believing Jesus told Joe to do polygamy .But Joe's own mom , son , & only wife swore he never did that sin .

We don't believe that , we don't believe everyone else will go to hell , and Joseph Smith was a true prophet

Don't get too excited about it. Of all the thousands of religions in the world virtually everyone of them thinks THEY are the only true religion and everybody else in the world is going to hell or will suffer for being one of them. If you think your job is to pick the RIGHT religion to avoid ever lasting suffering, you've missed the point.

All religions teach that.

Nope, he was a blatant con man and plagiarized extensively from the Freemasons and the religion he started is based on lies.  On the other hand, most Mormons that I have ever known have been really good people and I've never gotten the impression that they think their perfect.

Joseph Smith is no more a false prophet for Mormons than Mohammed is for Muslims or any prophet is for any religion. They might be false prophets for your religion but that is irrelevant, most people  don't follow your religion.