Why do many people think that top grand masters can always reach a draw? I often heard the claim that top grand masters can assure a draw, if they
 do not risk anything. I disagree with this claim.

What are the reasons that so many people think that very strong players cannot
 lose a game, if they do not play risky moves ?
The basic dynamic in modern top-level chess is that White wants to find a way to get some edge, often quite small, out of the opening. Black wants to find a way to equalize or otherwise draw. This means that a lot of what has been rejected by White are lines that lead to equality. So, I would agree that a top-10 player wanting a draw with White will basically never lose because he will simply select one of those ways that has drawn in the past. With Black, though, I disagree because making a draw is the essence of the challenge and often eludes even Carlsen.