Are we talking about aftermarket parts or clone/copy parts? They are very different things here and it seems like they're getting mixed up in this conversation. There's nothing wrong with aftermarket parts. They aren't breaking any laws and most if not all OEM car manufactures source parts from aftermarket companies. Almost all parts are made by another manufacturer. If you choose to buy parts from the dealer and pay markup for a branded box then by all means, go ahead. They are not made by said manufacturer.
As for clone/fakes. There is a difference. Clones are replicas made by a different company and branded as such. A fake would be something that's still branded as OEM but not actually made by them. I haven't seen anything like this in the RC world. So I think we are mainly referring to clones. As already mentioned, HPI doesn't even make the Baja anymore, so who cares? If they still made parts, the Baja clones would actually benefit them. When I used to own a KM Baja clone, I replaced most of the critical components with HPI parts. Sounds like a win for HPI. Manufacturers make way more selling replacement parts than selling the actual car. The KM Baja clone got me into 1/5 scale. After I sold it, I purchased a
Losi DBXL, a Losi 5ive and a used original HPI Baja. Buying a used HPI Baja over a new clone still doesn't benefit the original manufacturer in any way. They still don't make money off me for buying the car but in both cases (OEM or clone) they make money off me for me buying the original replacement parts. Aside from the MCD and Losi 5ive, I don't see any other clones out there. Aside from the Baja (mainly because the original is no longer an option), most people stay away from the MCD and 5ive clones. The MCD Rovan sells may actually be an original. The Price is very similar.
I've seen many cheap chinese 1/8 scale RC cars and trucks for sale and they are original designs. A lot of parts sourced from companies like Ofna, BSR and FTX. It might be a mish mash of parts from different cars, but it's still their own designs. Everybody starts off copying everyone, that's how they learn and develop their companies.