Supporters of this camp believe that Kurzweil is right that the singularity is near, but his proposed timeline is slightly overly ambitious.
Supporters of this camp believe in the power of exponential growth and the curve. But they believe that in several respects we may be further towards the beginning of the curve that Kurzweil thinks. This could cause the events of the singularity to take place anywhere from 10-100 years later than Kurzweil predicts.
For example, supporters of this camp might agree that exponential improvement is taking place in our ability to shrink our machines. However, they might question whether Kurzweil's extrapolation from the shrinking rate of transistors will carry over to the shrinking rate of self replicating nanobots, given that we have yet to create a self replicating bot of any kind. We can't figure out how far down the line of an exponential size shrinking curve a self replicating bot will be until we create our first self replicating bot and begin to shrink its size. Thus, although nanobots will eventually arrive, Kurzweil's projection is wildly overly optimistic in terms of predicting WHEN they will arrive.