EME strictly reduces the amount of "closed" code on the web. Without EME, more of the content protection stack is proprietary, and the trusted code base that enables content protection is larger. This is a very simple point that I think we all understand; I don't understand why EME's opposition thinks they can dodge it.
The assumption you make is that DRM _must_ exist in one form or another.
I, as an open web proponent, want to make it difficult for any business to add DRM to their media offering. by making DRM a difficult system to implement due to proprietary plugins, it increases the perceived value of just offering it without DRM.
but by having EME a standard, it makes it a no brainer to use DRM, because their customers will automatically have it as part of a browser. the cost of DRM is then externalised, and even legitimised such that it's the norm.
I have no trouble understanding the strategic goal nerds have of trying to use standards body formalities and browser vendors to retard the development of DRM software they disfavor. There's nothing wrong with that (at least, nothing more wrong with it than all the other things that are wrong with standards groups).
Where you lose me is the notion that there's an intrinsic ethical imperative not to provide attachment points in standards for DRM. That doesn't ring true.