See Forthodoxy’s outline of most issues pertaining to the matter.
[UPDATE: The site is defunct.]I do not agree with Yehudah B. Ilan’s conclusions, but all Torah questions require fresh, honest study, especially those arousing cognitive dissonance. We must, as part of the obligation to study Torah, continually reopen what grabs our attention and let the chips fall where they may. Too few Torah scholars today do so, relying on various slogans which reinforce unjust habit and Appeal to Authority.
An imprecatory verse from Pirkei Avos comes to mind:
ודלא מוסיף יסף
May the author be blessed with many more years and good health to uncover the truth in the Torah!
P.S., Why do I disagree? For one, modern scholars may add prohibitions of permitted activities to the Torah (as long as (1) they are self-consciously doing so and revealing the fact, (2) their reasoning is sound, and (3) there is no unjustified leniency or sin brought about through the new stringency). So Forthodoxy over here is correct, but incomplete.
Examples include not having the Shli’ach Tzibbur pray and say blessings for the congregation, since it is suspected that they do not listen carefully (unlike Chazal’s day), umbrellas on Shabbos (?), some laws of Bassar Bechalav, the Gaon on not going to the Mikveh on Shabbos, et cetera. Perhaps Rambam on Redid might be another (also relevant to Forthodoxy here. YB romanises it as “radhiydh”).
Do post-Chazal scholars keep up to the three aforementioned standards required? Not always.
There is more to say, but not now.