Flagging hits more than just low-value submissions.  People also flag totally valid submissions that they just disagree with (<a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=10819778" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=10819778</a> is a submission I distinctly remember this happening to).