Is it clear that they're not alike? In the end it's all information and data being processed, whether by silicon or neural cell. What difference does the medium make to the end result?

Then at the very least, you should be able to simulate a biological brain, neuron by neuron, and get an intelligent computer that way. If you agree that's possible, you also have to consider whether it's the most efficient approach -- plausibly special algorithms could be invented that get the same intelligence at a fraction of the computing power.