Namecoin isn’t a chainfork. It’s a legitimate altcoin, with its own genesis block, address prefix (preventing the loss-of-funds accidents so common with Btrash!), etc.; it’s also one of the few alts with an interesting idea, rather than being only a cheap imitation of Bitcoin. It can even be merge-mined with Bitcoin, such that shared hashrate can benefit both separate chains; indeed, Namecoin devs invented the concept of merged mining. It is not harmful to Bitcoin, or even unfriendly toward Bitcoin. Its goal isn’t even really to create a new currency, but rather, a new naming system which implements Aaron Swartz’s idea for squaring Zooko’s Triangle.
Actually, off the top of my head, it started with so-called “BIP 100” (not a real BIP number). Some old-timer or Bitcoin historian will need to correct me if I’m wrong there.
Regardless, as I said, the felons have learned. Early attempts only focused on overtaking the whole network all at once, directly from within. As I recall, XT tried (and laughably failed) to Sybil the network with a bunch of XT nodes run on cloud-computing machines, compliments of Roger Ver. I think eventually somebody realized the potential of using a separate forkchain for what trademark lawyers call “dilution” of a brand—thus, Btrash. Not that the total instant coup attempts have stopped; vide 2X, which is dead, but was only the latest in a long line of attempts at that kind.
I think the worst damage earlier coup attempts did was to (0) manufacture the blocksize controversy as an ongoing (and effective) propaganda ploy, (1) delay Bitcoin’s evolution, especially the activation of Segwit. Segwit should have been active on the network long before August 2017. We all could have benefitted from that. We are all at a real, direct loss from increased fees we paid, as well as opportunity cost.
Side note: I see a persistent recurrence of forum threads over funds loss from sending Bitcoin to a Btrash address (or vice versa). Also, I see threads discussing problems with trying to install both Bitcoin and “Bitcoin ABC” (i.e. Btrash) on the same machine; Btrash uses the same data directory as Bitcoin, and will happily overwrite Bitcoin files. Etc., etc. Btrash deliberately tries to cause as much confusion as it can, in as many damaging ways as it can.