1) Do you expect a single person to go through 1000's of documents with their rudimentary understandings and interpretations of the law? Would you and why would you trust him if so?
2) Should he have a lawyer go through the documents with him?
3) Should he get second opinions on whether or not something is breaking the law?
4) Should he trust a team of respected journalists and their team of lawyers to go through the documents on his behalf?
The journalists he released the documents to have trust that they've established for years. That makes them hard to dismiss as looney bins. Snowden does not have that trust and would have been easy to dismiss by himself.