Personally I don't believe in UFOs which is based on "faith" rather than evidence.
The arguments against UFOs are based on "argumentum ad ignorantiam" or "appeal to ignorance" which states the lack of evidence is proof for non existance. This is a logical fallacy.
Ironically science is attacked this way all the time. Creationists (or Intelligent Designists in disguise) frequently employ this logic.
Of the individuals in this group Alex is the main perpetrator.
Regards
Steven