As I said above, it's all about context and disclosure - and let me add reputation to that.
I was taught that online (or offline) success is/was based on trust. When you lose that, you lost everything.
Most famous people who write books name the other (real) author. I have much less respect for those who would try to hide that.
Sure, lots of wasted posts, junk and BS on my forums and all forums. The difference is that I don't pay for it.....nor put it there to look good.
It's an entirely different matter to have paid content - then again, some of the "content mills" our there are, IMHO, horrible business models over the long term and are, again IMHO, not worthy of the time.
We could write a book on this and I'm sure, depending on our situations, would have many points to disagree on. For instance, was it unethical for many sites to use Britney Spears in keywords way back when it fooled search engines? Is fooling search engines immoral?
The line is very different for each individual, company and situation - which is why we put in on the continuum of "ethics".