Why Is Obama Vetoing CISPA?

There's a bill that everyone hates called CISPA that Obama is supposedly going to veto, because he just really believes in "privacy, confidentiality and civil liberties safeguards."

There's an interesting precedent in history, when Harry Truman vetoed what is called the Internal Security Bill. It let the government target communists. Here were his stated reasons:

1. It would aid potential enemies by requiring the publication of a complete list of vital defense plants, laboratories, and other installations.
2. It would require the Department of Justice and its Federal Bureau of Investigation to waste immense amounts of time and energy attempting to carry out its unworkable registration provisions.
3. It would deprive us of the great assistance of many aliens in intelligence matters.
4. It would antagonize friendly governments.
5. It would put the Government of the United States in the thought control business.
6. It would make it easier for subversive aliens to become naturalized as United States citizens.
7. It would give Government officials vast powers to harass all of our citizens in the exercise of their right of free speech.

What's funny is the government at that point was in the thought control business, and the great assistance of many aliens in intelligence matters is one of the most horrible scandals of the country's history. So there's really not much information in Obama's reasons, is there?