Well, the simplest explanation may be: it's not correct.
He doesn't believe in functionalism (or at least he probably doesn't):
The question of uploading consciousness can be broken down into two parts: 1) can you accurately simulate the mind based on complete structural or circuit maps of the brain?, and 2) assuming you can run accurate simulations of the mind based on these structural maps, are they conscious? I think the answer is probably ‘no’ to both.
Perhaps he doesn't really understand the implications of universal computability. I've found that as a rule of thumb, almost everyone with a background in computer science believes in functionalism, as do most physicists, but it's somewhat less common for those with a bio science related background.
Someone can be an expert in the details of neurochemistry without having the slightest clue how artificial consciousness would actually work in practice.
Perhaps he doesn't really understand the implications of universal computability.
Or perhaps he's skeptical of the fidelity of that kind of model. Evolution famously abhors abstraction barriers.
Would you care to quantify your 'almost everyone' claim? Are there surveys, etc.?
Recently published article in Nature Methods on a new protocol for preserving mouse brains that allows the neurons to be traced across the entire brain, something that wasn't possible before. This is exciting because in as little as 3 years, the method could be extended to larger mammals (like humans), and pave the way for better neuroscience or even brain uploads. From the abstract:
http://blog.brainpreservation.org/2015/04/27/shawn-mikula-on-brain-preservation-protocols/