One of the most awesome gift given to us by God is the ability to think. With that power of thought, we generally start to dream. Also, people dream to give a shape to their hope,their aspiration. 
They say like Roosevelt said,"The future belongs to them who believe in the beauty of their dream". So, it's quite obvious that since one is free to dream and with so much collateral benefits, one should dream like Wright Brothers dreamt and enabled humans to fly.

But there is a catch,here too. With dreams, come expectations. Expectation is such a suicidal thing that it can tear you
apart by not reaching its destination.The moment you start to have expectations, the very moment you are always on its peril. As a youngster, you develop a dream, follow it trying to pursue it and gain expectation. If you are lucky enough to be able to achieve your dream, you will find another one,in it's nascent stage, standing there and waiting to occupy you further. And worse, if you fail to get what you dreamt for, you are crushed by the set expectations.

So, should we stop dreaming in lieu of all the arguments presented. Definitely Not. The flip side of it is much intriguing and inspiring. All the great achievers were great dreamers first. With no significant movement, the river also perish. Enjoying the extremes and living on the edge gives you the freedom to enjoy your life to the fullest.

"Where is the life we have lost in living ? " - T S Eliot