People do not dismiss UFO sighting as “conspiracy” as it says in your question as it currently stands. It is some UFO proponents who believe in a conspiracy: as in, the government is conspiring to keep the truth hidden, or an alien conspiracy has taken over the world. read more
Governments are very interested in any UFO sighting as it might pose a threat to their sovereignty and maybe the whole planet, so these things are investigated. Alas, all these serious investigations can't compete with all the 'UFO organizations out there'. read more
As (very little) research has revealed, the more recent hoaxes that have plagued the UFO community (and the events that are still 'in question') have been perpetrated by anonymous individuals -- which is why I disagree with the second statement. read more
Often lots of people do believe hoaxes. One of the most famous is the Spaghetti harvest April Fool in 1957. Back then we didn't have the internet and many people believed this hoax, especially as it was narrated by a very respected presenter in the UK, Richard Dimbleby, as respected in the UK as, say, David Attenborough is today. read more