I've always thought "character copyrights" made absolutely no sense, and have read through as many of the legal opinions on the matter as I could find, all of which defending such just seem like legal hand-waving. However, what it amounts to in my non-lawyer mind is a character is not a fixed and tangible work. In fact, all good characters (ones that are "protected" under the opinions mentioned above) are dynamic, developing changes over their literary lifespan. Further, no character is actually tangible.
When I was at the hardware store, the idiot behind the counter tried to convince me that I needed to buy a screwdriver when I already had a hammer. I told him that he and the tool industry wer demanding twice the workload from me in order to fasten two objects with a piece of metal.
I've been using hammers and nails for as long as I can remember, and now I have to use screws and a screwdriver? Plus, I hear they have TWO DIFFERENT KINDS of screwdrivers. Why should I have to massively increase my overhead when a hammer can already be used on nails and nail-shaped objects?
I think that the reason why tarnishment is a valid thing is because most consumers say to themselves: "Oh, how could Company X let Company Y use their name so immorally?" without considering for a moment that this is either an unreasonable expectation on Company X, or an unreasonable expectation on everybody else.
It seems to me to be a consumer confusion problem, but one that's been promoted by these big companies.