NPAPI plugins are already ActiveX in the browser by your definition: technologies controlled and pushed by a single vendor. In fact, they're even more like ActiveX than NaCl is: they're generally closed-source, vulnerable to a wide variety of exploits, and in some cases not even cross-platform (Silverlight, for example, is a closed-source Microsoft product that "extends" the web and is not released for Linux). Moving to NaCl is better in those senses than NPAPI-based plugins: if the plugins are written in NaCl, they'll at least run on every major OS, and be sandboxed safely.
And NaCl isn't the only recourse for previously-NPAPI-based plugins. It's just the worst (for the web) choice. Better is to build the plugins on top of JS, which some vendors are already doing: for example, the announced future of the Unity on the web is compiling to JS.
Non-web-technologies (like the current iteration of NaCl) intruding on the browser is bad for the open web. But plugins are also bad for the open web, and deprecating them is better than not deprecating them. You can't fault the Chrome team too much for closing one door just because they left another open. :)
And NaCl isn't the only recourse for previously-NPAPI-based plugins. It's just the worst (for the web) choice. Better is to build the plugins on top of JS, which some vendors are already doing: for example, the announced future of the Unity on the web is compiling to JS.
Non-web-technologies (like the current iteration of NaCl) intruding on the browser is bad for the open web. But plugins are also bad for the open web, and deprecating them is better than not deprecating them. You can't fault the Chrome team too much for closing one door just because they left another open. :)