If they don’t exist, then how did they end up in different cultures all across the world? Unless everyone had observed the same thing, or else dragons would only be a minute part of a certain civilization.
Cultures and civilizations all across the globe are separated by distance and time. They are uniquely defined in terms of knowledge, philosophy and fate. Some went extinct; some invented the compass; some created paper. Yet all of them have one thing in common; the existence of a ferocious, fire-spitting, huge serpent-like creature, and with its wing(or no wing) it could soar thousands of miles, spreading fear into the communities below.
Assimilation of culture is limited to certain civilizations, perhaps connected via trade or exploration. For example the Indian and the Chinese were connected via trade, and as a result Buddhism was brought to China. But lets not forget that the Greeks and Eastern Europeans also have their own version of dragon which is almost identical to the dragons of India and China, and they had never crossed the vast Steppe and stepped into China.
In Europe, dragon is the symbol of fear and evil. No one wishes to see a dragon, lest get devoured alive. Kings and the nobles favored the slaying of dragon, even when the dragon is not destroying villages and towns. Stories of dragon slayers were popularized and heroes were hailed as saviors. In the bible, the dragon is the symbol of the Devil himself. This concept was made eminent by the Catholic Church during the Dark Ages, in their endeavors to manipulate the people around them to be dependent on God.
In India, however, the dragon, called Naga is regarded as god. This is the same word incorporated into the Malay Language. The Indian merchants brought their culture with them when they came trading at the Malayan Archipelago centuries ago, leaving an everlasting impact within the communities of this region. The ancient kingdom of Lembah Bujang, Srivijaya, and Majapahit were all under their influence, worshipping Hindu deities and incorporated the term “Raja” which means “King”.
Naga and Garuda engaging in a war
Ancient Indian myth tells of stories about how Naga came about. From the Indian epic Mahabharata, it is said that Naga was born the cousin of Garuda the giant eagle.
Eventually they became enemy due to certain dispute and Garuda vowed to treat Naga as food. That explains why eagles eat snakes. And that also shows that Naga is in fact the King Cobra.
Vishnu, one of the gods of the Hindu Trinity, finds shelter under the hood of a King Cobra. That elevates the status of Naga to that of a god.
In China, the dragon is also regarded as a symbol of power, wealth and prosperity. The king of the sea, “Hai Long Wang” is a man with the face of a dragon. His army is made up of creatures of the sea, and he lives thousands of feet under the sea within the serenity of his palace. He dictates the changing of weather and water, and being a god he is often portrayed as selfish and inconsistent(from what I’ve seen on TV, might not be true).
Another version of the Chinese dragon is the Chinese Fireball Dragon. According to some sources the female fireball dragon is larger in size than the male. It lays eggs that are crimson in color and have specks of gold scattered all over their surface. The legend that surrounds the story of the Chinese fireball dragon tells us that the shells of the eggs of the dragon are desperately sought after by wizards. The fireball dragon feeds on mammals and its favorite items on the menu are big and juicy pigs and human beings.
Even the learned Greeks admit the existence of dragon.
Ladon was the serpent-like dragon that twined round the tree in the Garden of the Hesperides and guarded the golden apples. Ladon was also said to have as many as one hundred heads. He was 
overcome and slain by Heracles.
The Lernaean Hydra
The Lernaean Hydra was a dragon-like water serpent with fatally venomous breath, blood and fangs, a daughter of Typhon and Echidna. The creature was said to have anywhere between five and 100 heads, although most sources put the number somewhere between seven and nine. For each head cut off, one or two more grew back in its place.
The dragon of Egypt is called Apep, the dragon of chaos. Apep was also known as Apophis, Aaapef and Rerek. Some people, however, preferred this serpent-like dragon to remain Nameless.
Dragon of Darkness and Chaos, Apep. Picture:susanneiles.com
Mesoamerican Civilization
More amazing facts await you across the Atlantic Ocean. The Mesoamerican civilization, separated from the rest of the world, also have their version of dragon.
“Also known as the Earth Monster, the Olmec Dragon has flame eyebrows, a bulbous nose, and bifurcated tongue. When viewed from the front, the Olmec Dragon has trough-shaped eyes; when viewed in profile, the eyes are L-shaped. Fangs are prominent, often rendered as an upside-down U-shaped bracket.”
Again we could a common trend within all these cultures; they claim the existence of a giant serpent-like creature, ferocious and brutal.
If a dragon does not exist, what makes these people believe that it does?