This is about the Web USB API, not the entire web in general. Are you routinely granting web pages access to your USB devices? That's not a permission that web apps get by default (unlike with native desktop apps btw).
It comes down to this: if you ever found yourself in a situation where you needed to connect a USB device to a remote service, would you prefer to download that service's unsandboxed native code to your PC and execute it? Or execute some JS in the browser sandbox and grant it limited access to that one specific device?
Would that include the "Run" button on a downloaded executable?
While obviously we want to do as much as we can to discourage users from shooting themselves in the foot, there are limits. At some point, eventually you _do_ have to trust that the user knows what he's doing.
Giving users a choice on when to allow a page access to one specific USB device is not a "disaster".
It comes down to this: if you ever found yourself in a situation where you needed to connect a USB device to a remote service, would you prefer to download that service's unsandboxed native code to your PC and execute it? Or execute some JS in the browser sandbox and grant it limited access to that one specific device?