If Rama is not myth then he must be a human being. Then the stories depicted in Ramayana (like Pushpak Ratha, Hanuman's sea crossing, Ravana's 10 faces) are only imagination in the backdrop of social condition at that time. If Rama is God then he never came to this earth physically. He remains in the minds of the believers. All the rivers,mountains,volcanos,were the outcome of natural evolution of Earth. 'Ram setu' would have been created by the same process.
We go against nature like constructing a dam across a river when it is necessary to control floods or bring economic prosperity even if it is a sacred river like 'Ganga'. Similarly if by constructing a canal of 300 meters wide canal which will intersect 'Ramsetu' of 35 km length to bring economic prosperity to the country then what's the harm?