Explain the use of the broom in curling to me

[bouv]

OK, first off, I know why they use it...sort of. It roughs up the ice, which in turn slows down the stone, that way, they can hopefulyl have it stop where they want it, or have it hit the other stone they want it to at the right speed. My question, however, is this:

Why don't they just not throw the stone as hard?

I imagine that when starting out, one is unfamiliar with the behavior of the stone on the ice, but after being in it for many years and being a pro, shouldn't they be good enough to just know how hard to let go of the stoen so it hits what they want it to with the right speed? To compare, after many years of playing pro darts, one would know at what force and angle you need to throw it to get it to land where you want, so why isn't it the same with curling? Aren't they basically just taking the easy way out? (In that rather than build the skill of releasing the stone, they'd rather just use a broom.)