I can argue both sides of this one: First, they can-not reproduce new saws because of patent protection, so let's talk about reproducing parts for old saws like MS 440, 460 and 660.
If the OEM companies did not rape you on the price, you would not bother with second rate AM parts, but if you need a tank holder, carb and coil to fix an old saw and the OEM parts are $180, $160, and $150 respectively, you are either going to find cheaper parts or not fix that saw. There is NO REASON parts for 20 + 30 year old saws should cost so much!
Folks willing to do the work to bring a good saw back to life should not get raped on the price of parts. That is why I will not feel guilty about using AM parts to restore a saw (or complete saw kits to learn about building and porting saws).
I own several new and old OEM saws, I own several fully AM saws, and I own several that are a combination of both.
One of my favorite saws is a 440/460 ported hybrid that pulls a 28" bar buried in hardwood like a gangbuster. It has an AM case and main bearings, tank holder and plastics. The crank is from a 12mm 044, it has an 046-D jug, and a Husky single ring piston (to allow for wider ports, and it is lighter weight than a OEM 460 piston which reduces weight and vibrations). The carb is an OEM 70 jet, but the intake and impulse line are AM. The saw is an animal and I love it!