Complex sentence: Some compared any continued belief in UFOs as an unusual phenomenon to those who insisted the earth was flat; others predicted that interest in UFOs would wane and in a few generations be only dimly remembered, like relics of spiritualism such as ectoplasm or table-raising.
Split into simpler sentences: Some compared any continued belief in UFOs as an unusual phenomenon to those who insisted the earth was flat. Others predicted that interest in UFOs would wane and in a few generations be only dimly remembered, like relics of spiritualism such as ectoplasm or table-raising.