As I am interested in all theories of evolution. And believe nothing is immpossible.
When it comes to evolution. Mother nature has its way of obstrucking humans present theories.
My main concern of this theory. If mermaids are real. Can we look at what man has done to dolphins. Will humans explot such creatures,  which is more than likely our ancestors? In the name of religion and war.
Would we show them the corruption of human nature on land. By using these creatures to benifit Our Military.
And would the Government or Military reunite this creature with its vast chain of ancestors.
Or would they just simply explot them for the Bettering of National securities? Like the dolphin.

If they do exist all humans must stand. And protect these innocent creatures that chose the Ocean as we favored on land.
The advancement of technology would be much harder in bodies of water. And they may never have a chance to advance. 

Should we help their advancement?

Look what we have destroyed in our past. Many Cultures, Ancestors and Creatures.
My aunt told me as a young child. One day when technology has advanced. That we may really see true Mermaids. Was she a prophet or did she understand how evolution works?
Funny how things get lost when people pass to the other side.

If they have survived this long without us. Then Infinitly we will destroy them. As we look back at our violant past towards mindkind himslef.
For their sake I hope it is MYTH. But we can not allow the possibility of ignoring them, because the past and present of our government making wrong decisions.

http://theclicker.today.com/_news/2012/05/30/11955621-were-you-fooled-by-animal-planets-mermaid-special?lite

http://www.christianpost.com/news/mermaids-are-they-real-animal-planet-special-debuts-discovery-video-75727/