Politicians have more to their agenda than helping the general public. They want to stay elected. They can be bribed. A decision made with direct democracy will match public opinion much better than a decision made by representatives. Just look at SOPA and PIPA. Public opinion was always radically against these bills, yet a significant proportion of representatives supported them.
I don't think there should be any type of direct government anywhere, let alone direct democracy. California is a great place to live and to have one state in the United States be subject to direct democracy would be unjust. Why should one state face direct democracy when all the other states don't .
California doesn't need a direct democracy, and neither does the United States. For the past 200 years, the U.S. has run as a representative democracy. California has followed the same principle for decades with decent results. There's no reason to change the system so drastically at the present point in time.