Well, there are many different possible levels of brain emulation (just like in emulating video game consoles), all of which have different demands and feasibilities. The Whole Brain Emulation roadmap discusses several.

No one denies that details of every molecule would be a very brute force and difficult emulation and as far as that goes, he's not strawmanning; but to think that this is the only kind of emulation and dismiss emulation in general on the basis of the specific, that is a straw man.