If the strength of the magnetic field is substantially reduced during the shift it could mean higher exposure levels to high energy particles. It's not BS but it is something over which humans have absolutely no influence or control. Although I don't doubt Al Gore will blame America and try to find a way to make a few million bucks off it.
As you so correctly point out, the Earth’s magnetic poles occasionally reverse. This fact is recorded in the magma released on the Atlantic sea floor due to plate tectonics along the Atlantic Ridge. It turns out that iron crystals in the molten magma align with the poles when in their molten state and are forever frozen in alignment when the magma solidifies. Sensors on board ships and submersible sensor pods can measure and record this alignment and the record was used to confirm the theory of plate tectonics.
None of us alive today were around the last time the poles reversed, in fact that event lies outside the range of recorded history. None of use know how fast this happens and what the signs of reversal might be. None of us know how quickly it proceeds and what the effects might be on our protective magnetic shield. This is the realm of speculation, some of it informed by physicists and other scientists much smarter than any of us can imagine.
No matter, there is today some Freeper, probably living in his parents basement, who has figured this all out and we will be regaled with a blast of the truth unrivaled since the Obama birth certificate revelations.
Boy that second picture can’t be good for navigation or modern weapons systems!