I'd prefer a more neutral option...
I lean more towards "yes"
Firstly, given recent events, I no longer have much support or respect for copyright.
I will say is that credit SHOULD be given, but even THIS is bit iffy. Some of the protected images I've seen quite frankly don't merit ANY kind of protection on them, and people should be able to use and trace as much as they want. (Mainly seen this in some stock vectors)
I feel there are many legitimate reasons to trace or heavily reference another artist's style. Also, depending on what you're making your piece for, you may WANT to create something that feels related to the original work. For example, let's say I was hired by Nintendo to make sprites/models for the next Pokemon game. It'd make sense for me to study/copy some of the previous sprites and models, because that is what Nintendo, and the fans, are expecting, consistency. I actually have a few projects that require a certain level of consistency with the works from which they're based. Some of them pretty much need the originals. However, credit will be given where it's due, and can be given (some people don't put credits on their works, so i can't credit them >.>) One of these projects I do actually have permission to use some of the original works as-is, though I still am doing my best to create my own, anyways. Another thing which I AM going to submit here if I EVER finish the trace, was a piece of desk-art I encountered in school one day. However, still not claiming as my own, just going to credit it to some anonymous person, since...NO IDEA who drew it (INSTEAD OF DOING WORK)
Tracing also can be used to develop a personal style, since one could trace/heavily ref. various art styles, and get a feel for what they want to see in their art, and what they can even accomplish. They could even trace an artwork in their own style to see how something looks in it.
The ONLY strict rules I can think of is not with tracing itself, but rather, attribution...
When possible, CREDIT THE ORIGINAL PERSON
DO NOT claim as your own (excluding some VERY rare circumstances that I'm not going to bother explaining)
Ask permission if/when possible
Well, in the case of dA... don't submit them here, I guess...but that's mainly to not get reported by some overly righteous copyright troll up on their high horse.
ABSOLUTELY, FOR NO REASON WHATSOEVER, SHOULD YOU MONETIZE YOUR TRACINGS
Oh, and one last major exception, or at least, it makes sense:
If someone sells/trades/grants request of something to you, pretty sure you now own that design/work. First thing I did to my Secret Santa gift was trace it, mainly to enhance it, since... photo quality generally equals shit. Even so, if someone designed it themselves, should still give credit, and I DID in fact, link to the original.