Edit: Some back of the envelope calculation suggests that the total cross-sectional area of all man-made orbiting satellites is around 55000 m^2. Just one 4km x 4km = 1600000m^2 starcloud would represent an increase by a factor of about 300. That's insane.
e.g., Cianide seems bad, but it won't kill you if the relative volumes are small.
tl;dr: You haven't characterized the denominator.
> increase in a risk factor of over 300
Even with a numerator-only view, I suspect it's not fair to characterize the "risk factor" as going up 300x. There's a lot more nuance about orbits in space.