Overload: The danger that too much information will cause humans to miss the subtleties and overlook important ideas.
Culture Lag: The time that it takes human society to catch up to the new ideas revealed by extraterrestrials.
Lack of Understanding: There would be clear dangers in humans failing to fully understand the information and trying to reproduce technology. Mistakes could be disastrous.
Losing our Curiosity: If we are spoon fed the secrets of the universe (at least as known by this particular extraterrestrial civilization or group of civilizations) will we lose the initiative to explore and learn on our own?
All of these concerns raise the need for intermediation. A data dump of information would be incredibly tough for humans to decipher and could have many negative consequences. If the extraterrestrials are far in advance of us in terms of technological and social development, we may need to be schooled. The information would likely be complex and need explanation. Extraterrestrials would be the only ones capable of doing this. Whether they would want to educate us is another matter entirely.
How would we react to being students? Several authors in the Foundation For the Future report discuss the impact to the human psyche. It seems plausible that human society could suffer from a collective inferiority complex After First Contact. We could go from being the lone masters of the universe (at least in our own minds) to relative babies in terms of scientific knowledge and technological prowess.
The actual impact of First Contact could depend on how the entire process for diplomacy and knowledge transfer goes forward. In addition to safeguards through information gatekeeping, both on the part of extraterrestrials and humans, it would seem important to make the celebration of being human part of the larger context. We must learn to appreciate what we have and what we hold valuable as humans. Then we need to realistically understand our place in the larger scheme of things. One can only submit to being a student when they are confident in their talents and truly ready to listen and learn.