I see no logical reason to argue that a reproduction of an old piece should not be marked by the current day manufacturer..... It is a reproduction, and as such will not be value diminished by clearly marking it underfoot.
Not doing so dilutes the market for the original pieces, and does a disservice to the less knowledgeable collector, allowing unscrupulous dealers to take advantage of their lack of expertise. Understanding that the issue at that point is the unscrupulous dealer, I believe the manufacturers are contributing to the issue by producing an unmarked reproduction that can be misrepresented.
If I as a manufacturer have a reasonable suspicion or knowledge that my product may be used to deceive, and I do nothing to prevent it, then I share a portion of the blame due to my inaction. If I am proud of my reproductions, I should not have a problem "branding" them with my mark.
In the law, if it were a crime we were talking about, the term would be contributory negligence.... Simply taking the position that they can not control what sellers do later, is not a viable position. Especially in light of the fact that a simple mark underfoot could help to reduce the problem substantially.
Ebay tried that position (we can't control what sellers do) with Vitton, Tiffany and others, and it cost them tens of millions of dollars.... they were found to be contributing to the problem through inaction. I do not really see much of a difference......
Craig