There are two camps to the UFO subject: those who agree they exist, like people agree Antarctica exists (although they've never been there); and those who believe they exist, because they want there to be something more than us.
The first camp would stop agreeing they exist the moment they're shown not to; the second probably would not stop believing in that case.
Personally, after having read a lot of material on the subject, I am still keeping an open mind on it. I think it's a fun thing to read about; one of the most entertaining sources I've come across is Wendy Connors Faded Discs CD recording of reports to the National UFO Reporting Center in Seattle. It's a historical audio account dating from the 1970's on, and it's 44 hours of spooky fun.