One of the central motifs in the debate surrounding 'Post-Orthodoxy' is the apparent 'pushing of the Halakhic envelope' on different issues. The objections have different emphases and nuances. (Please excuse the repetition, since I've touched on these issues before.)
Some point out that there is a fundamental dishonesty in this envelope pushing, since we often see the pushers cobbling together scattered sources to support a specific (not clearly indigenous) agenda. Others emphasize the increasing decline in respect and deference that is accorded to recognized halakhic authorities, as each person seems to chart his/her own path in observance. Then again, in many cases, halakhic innovations crudely ignore the critical role of consensus in halakhic discourse (סוגיא דעלמא).
As readers of this blog know, I have noted (and agreed) with most of these objections on many occasions. It is arrogant to foist an outside agenda upon the body politic of Judaism. It is arrogant for less than qualified individuals to arrogate rabbinic authority to themselves, just because they possess basic Jewish (or rabbinic) literacy. Selectively citing sources, while ignoring the weight of rabbinic tradition, is a violation of the texture and essential dynamic of Halakhah, from Talmudic times until today.
However, let it be noted that many of these objections can be just as easily posed to the so-called Right as to the so-called Left. The culture of humra, the abandonment of established halakhic traditions and practice on the grounds of contemporary inadequacy (aka מיר זיינען גארניט) and the denigration of women are just as much a deviation from hoary halakhic norms, as the innovations flowing in from the Left.
The same is true in the area of theology, though here Left and Right mirror each other. The Left goes where no Orthodox Jew has gone before, while the Right so narrows the field of what is legitimate and what is not that many great scholars of the past (including Rashi, Rambam, Ramban, Rashba, and Rema) would be excluded from Orthodoxy.
Apparently, Post-Orthodoxy cuts both ways.