As it happens, I readily admit the possibility of lake monsters although Nessie is getting rather long in the tooth. But that does not make me a "believer". I am very skeptical by nature and suspect most sightings are misidentifications of other large creatures (but I would be tickled pink to be wrong on this one). I think few people can go through life both without being fooled at least once and without encountering something they cannot explain.
On crop circles, I see no other explanations worth considering. And clearly, the more complex they are, the less likely is a natural explanation other than mankind. And, so I really do think that art is the point.