I agree with your opinion on curves (which aren't even a thing where I'm from), but cheating matters even in the absence of curves.
If GPA is a factor to achieve certain jobs, positions, grants, PhD programs, etc. (which it obviously is, to varying extents depending on countries, but AFAIK it always is) then someone who is inflating their GPA via cheating can basically "steal" your job/PhD/etc., curve or not.
If GPA is a factor to achieve certain jobs, positions, grants, PhD programs, etc. (which it obviously is, to varying extents depending on countries, but AFAIK it always is) then someone who is inflating their GPA via cheating can basically "steal" your job/PhD/etc., curve or not.