<p>If a comment is not constructive, then flag it as such.</p>

<p>It seems to me that your wording "<em>this comment is inappropriate and/or does not add to the discussion</em>" is, for this purpose, a different way of saying "not constructive".</p>

<p>Non-constructive comments are clutter that should be removed. So they're qualitatively different to incorrect answers. Hence there's a flag for them, rather than a downvote button.</p>
