I understand grading on a curve. This is not that.

What we're talking about here is remapping a fraction (what the student scored) to a higher-than-equivalent percentage (what the "standard" requires).

it was used by many of my math & science classes here in canada, and i'm unsure why it is a problem?

The prof would make the test very hard so the average was around 50-70 and then use a curve to get grades.

Curve grading is just conceptually silly. If a test does indeed cover the material, then answering correctly half of it should lead to a 50%, no more, no less.

If curve grading is required because the test doesn't properly assess what the students have been working on, that means the test was bad in the first place.

In my first semester (I think, might have been second) honors calculus class, the (great) teacher got carried away on one midterm. I got something like 40%, and that was the second highest grade in the class, the average was more like 30%. He was so disappointed we didn't do better on that exam...