A human's short life span and humanities relatively  short history give us an unrealistic perspective on many things. We tend to think of the earth and it's natural functions as being more or less static. Nothing could be further from the truth. 
Building cities/towns at the waters edge is no different than building sand castles at low tide. You shouldn't then be shocked when the sea level then changes.
As long as there have been seas, the sea level has been changing, to think we can stop that is the same as thinking we can hold back the tide.