Have extraterrestrial beings ever visited Earth?

I'm referring to intelligent extraterrestrial beings (aliens, not micro-organisms). There seems to be a lot of personal accounts, photographs and actual items (whether accurate or not) supporting the evidence that extraterrestrial beings have visited earth, along with ancient civilisations and records having... show more I'm referring to intelligent extraterrestrial beings (aliens, not micro-organisms).

There seems to be a lot of personal accounts, photographs and actual items (whether accurate or not) supporting the evidence that extraterrestrial beings have visited earth, along with ancient civilisations and records having information regarding aliens.

But there also seems to be a lot of people who completely disregard anyone who says aliens have visited earth and call them delusional or insane.

My question is - can someone please give the best explaintation they have for believing that aliens have visited earth or that aliens have not visited earth with reasoning behind your answer or opinion?

Because I really don't think THAT many people can have common physical symptoms, thoughts and experiences or them to be ALL real (it's very obvious some are hoaxes) or all of them to delusional or insane.

There must be more to it - or another explaination at least.
Update: I'm serious about this question, and I'll be picking the starred question, so the person who gives the best reasoning behind it will probably be chosen. :)
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