That is in the context of learning. You will never find an artist who thinks it's ok to trace another's work, claim it as your own, and then sell it for profit.
As mentioned, I'm not starting a debate, but it seems fairly obvious from the discussions among professionals I referenced that at least some aspects of tracing are considered professional tools and are valid.
Not as a learning exercise, but as a time saver.
Now, it's equally obvious from that and the other pages I found that opinions vary and that there are lines, but the consensus seems to be that the basic of tracing, then adding you're own shading and work is something that is done in the professional arena, and it didn't take a lot of googling to clarify this.
At a minimum, the consensus opinion among the professionals is that it is not in and of itself a violation of ethics.
Now, I don't know if what Bo Wei did exceeded what was discussed in the threads I found, but what was *described* did not.
I personally have a fairly educated layman knowledge of IP law and was a bit surprised at how casually the threads considered it ‘fair game’, so it seems feasible that some people had opinions about what they would consider wrong that they considered self-evident and thus never researched.
So... Just don't assume that what seems self-evident is actually quite as big an issue as it was presented. Do some googling.