Original_Sin
Clark Kent, as has been shown in Smallville, has always struggled with who he is and what he is capable of doing. Being able to let that part of him out for the world to see is what gives Clark the ability to be "normal". He couldn't be one without the other. Being just Superman would drive him nuts. Being just Clark would do the same.
I concur. His persona 'Clark Kent' allows him to mingle in human company without consequences. It allows him the chance to be 'normal.' But he wouldn't be satisfied with
just being Clark Kent. Clark has an inherit leaning towards good, and it would eat him up in side knowing he could do something about all the horrible things happening in the world and then not doing so. As 'Superman' he can use his powers without repercussion; he can help people and still have time to himself. If he were strictly Superman he would loose all sense of himself; that part of him that makes him "human" as you will. The responsibility is just too much to lay on one person -- even an alien. So: he is both Clark Kent and Superman, and at the same time neither. As a person, behind the masks, he a unique blend of what makes him great and what makes him human.