A number of objections have been raised to the possibility of Artificial General Intelligence being developed any time soon. Many of these arguments stem from opponents directly comparing AGI to human cognition. However, human cognition may have little to do with how AGI’s are eventually engineered.
It has been observed that since the 1950’s there have been several cycles of large investment (from both government and private enterprise) followed by disappointment caused by unrealistic predictions made by those working in the field. Critics will point to these failures as a means to attack the current generation of AGI scientists. This period of lack of progress is referred to as the "A.I winter".
Furthermore, a variety of high profile figures from computer and neuroscience, such as Steven Pinker and Douglas Hofstadter, have suggested that the complexity of intelligence is far greater than AGI advocates appreciate. Even if computing power continues to increase exponentially this does nothing to help with understanding how we might build an AGI.