I don't think many people are unaware. Sometimes when I see dead comments I trace their comment history back to the point they were banned. Cause I'm curious how those subterranean dwellers got that way. Almost invariably they were reprimanded by dang, repeatedly, and refused to change their ways, or to write to HN saying they'd change their ways. I don't recall seeing someone just mysteriously banned without an obvious refusal to behave decently/put some effort into their comments. The white dead comments don't start at some random point, they start with the person being told they are banned, and what to do about it.
Although I did see a fairly new account the other day with every comment dead, from the very first one, with no visible mod intervention; I figured it was from being a sockpuppet or someone with a track record.
p.s. I wouldn't want showdead on all the time! I use this "HN ungrey" bookmarklet to see whited-out comments on a page. Also it's useful to read comments that have just been voted down enough to be hard to read:
javascript:(function(){var i,x=document.querySelectorAll(".commtext");for (i=0;i<x.length;i++) x[i].className='commtext c00'})();
For other sites–on the topic of useful bookmarklets–this one, "Kill Element", is a lifesaver. On any site with an annoying fixed window thing on the screen, like a "cookies?" popup etc, just click on the bookmarklet then on the offending element and it disappears! Hugely satisfying, and instant. Enjoy!
javascript:for(var i=0; i<(document.getElementsByTagName('a')).length; i++) {(document.getElementsByTagName('a')[i]).style.pointerEvents = 'none';}function handler(e) {e = e || window.event;var target = e.target || e.srcElement;target.style.display = 'none';document.removeEventListener('click', handler, false);cursor('default');for(var i=0; i<(document.getElementsByTagName('a')).length; i++) {(document.getElementsByTagName('a')[i]).style.pointerEvents = 'initial';}}document.addEventListener('click', handler, false);cursor('crosshair');function cursor(cur) { document.body.style.cursor = cur; }