Why do you insist that mermaids don't exist even though there are many stories and sightings?

There are many stories about Santa Claus, Big Foot, and the Easter Bunny, so many stories about something doesn't automatically make it true. When it comes to sightings, people see whatever they want to see. That is how the mind works. Look at the clouds long enough, and you will recognize the shapes as other objects. You will see animals, vehicles, tools, and even Words in the clouds.

Unless mermaids and mermen are some sort of aliens, their existence is scientifically impossible. Humans and fish cannot mate and breed together. There are different chromosomes.