There are a couple of things going on in that episode, from what I recall. CreationEdge is correct, it's important to know that the dream was sent by Shifu and Oma, to discourage the use of Harsecis memories - so it didn't have to be faithful to his character, it had to fit into the lesson he was being given.
One part of the lesson was about trying to use Goa'uld knowledge, and power - from what I remember of the episode, the military wanted to encourage Shifu to access the memories, so they could pull tactical data and technology, and Daniel seemed open to being persuaded by the good that might come of such knowledge at that point.
However, getting access to the Goa'uld knowledge to recreate technologies was not a simple matter of calling up plans on a database. The knowledge was tied to genetic memories, and those memories were intricately interlinked with memories of Goa'uld customs, culture, attitude, and probably emotions, as well. Shifu believed that his trying to access the memories meant exposure to, and the risk of accepting the cultural memories and attitudes long before gaining access to any technological memories. The Tok'ra accept the culture and history, and find an interpretation that's (maybe) not evil - and as children of a single queen, there is likely a genetic component, as well. Other Goa'uld would grow up with the memories, and might, as adults, come to a different conclusion and find a different way. As a child, Shifu believed he would not have the strength of personality, or the weight of his own memories and life experiences to balance the weight of the genetic memory and keep himself whole and human.
So part of the lesson to Daniel, was about the things that might come with the memories that none of them were considering. Shifu was trying to show that if an attitude or mindset came through with the memories, it would be very difficult (or impossible) to tell from the inside - and maybe hard to tell from the outside until a great deal of damage had been done, if it were subtle enough. Other sources of technology or power might not be as risky, if they don't have that extra baggage or direct access to someone's mind to rewire it.
The other part of the lesson, I think, was one of consent. The military, and Daniel, were not actually risking themselves to gain access to the memories, they were risking Shifu. It would be possible to contain Shifu so that even if he did lose himself he didn't have the opportunity to cause harm - but that would not be right, they would have used him for the information, then confined and limited him for risks that they chose for him. Shifu was a child in Daniel's care, it was his responsibility to do what is in Shifu's best interests. Gaining access to the memories might help Earth, but it would be at the cost of betraying that responsibility and sacrificing a child.
That is the other part of the lesson, I think. The dream didn't show Shifu going off the deep end, after all, or pointing out how much damage he could do with the goa'uld knowledge inside him. Instead, Daniel, who was being persuaded in that episode to let them use Shifu, gets to experience what it might be like to gain the power but at the cost of a corrupted mindset. Daniel gets to be afraid of what he might do if he had access to that power, not so that he won't go looking to use the Goa'uld memories, but so that he won't make the choice for someone else.
And, as a bonus, by painting the power taken from the Goa'uld memories as itself corrupting and dangerous, it lets Daniel use that idea to persuade the military that the technology would damage whoever uses it, not only whoever had the memories to begin with. That might have encouraged plans to keep Shifu himself in line and not let him get into a position to cause harm, instead of looking for alternate sources of technology.
Actually, I think the Ascended might simply believe that power itself corrupts - it would explain why they have a strong belief in not interfering even when they could do good, or even if the problem is their fault (as later seen with Anubis). So that part of the lesson would come from Oma, not just Shifu - to deliberately discourage the use of Goa'uld technology, or any technology or power, as evil or corrupted - whether or not that is actually how the power is going to be used.