Diverse code ownership is a security issue. Even if the OS code is just as "good" as the browser code (and there are reasons to believe that's not necessarily

Diverse code ownership is a security issue. Even if the OS code is just as "good" as the browser code (and there are reasons to believe that's not necessarily the case), the assumptions is makes are at least partially encoded as knowledge by the authors. When you're dealing with benign code, that's no problem - people work around OS/library bugs and/or (mis)features all the time - but if you're going to expose the code to potentially hostile third-party input, it's a little tricky. There's simply more opportunity for miscommunication when there are multiple parties involved and the spec is complex and may lend it self to native (unsafe) implementation for performance reasons. Browsers are right to be hesitant, here. Frankly, they should be hesitant, and sandbox the plugin, and use something like rust, and even then I expect there will be exploits sometimes.