The comment in question - go read a few pages of the poster's comment history and you will understand it was meant as sarcasm. The difficulty is that sarcasm takes social capital to execute, and the comment-in-isolation model eschews even having that type of reputation.

Now in this case it would have been relatively easy to avoid sarcasm (although tiring, and I would say we're worse off for it). But the same difficulty applies to straightforward communication as well - if someone is criticizing the DNC, are they doing it from a place of trying to reform and make it better, or are they trying to drive cynicism and apathy? You don't know unless you know them.

And while you can mitigate the problem by writing comments that appeal to some groupthink (marking you as part of the tribe) before making a nuanced point against some other bit of groupthink, this propagates the first groupthink (which is itself often a problem) as well as bad-faith commenters being able to perform the same pattern.