Because if we do it this way, we won't need "showdead" any more: "dead" posts will work naturally no matter what your settings are. There's no reason to have an advanced setting to allow you to click through to a dead comment; everyone should just be able to do it.

It also neatly dodges the problem of deemphasizing toxic posts on threads; the content simply isn't displayed in the thread, but is available in a more readable form just a click away.

It will also do nice things for the formatting of the threads themselves (flagged comments on nested threads won't take up much vertical space).