this question is kinda confusing...
having a clean conscience means being a saint or being a baby(literaly)...
once you learned things,you're no longer innocent.and it'll be hard to be completely clean conscience,for example,you saw your friend cheating on a test,what would you do?whatever you do,you wont have a clean conscience,if you tell the teacher,you betrayed your friend,if you didnt tell the teacher,you still have no clean conscience,since you hid the truth...
basically,i think no1 is trully clean in conscience,but it never meant that you are an evil person,it's just about how you live your life,and what you do in life.there's no real way to know if what you believed in or hold on to is right or wrong.all in all,in death you will realize wether you lived your life at the fullest or you missed alot of things...
though there's nothing wrong about being totally honest or being pure,but it'll be hard to be one,specially in our world and age...