Can one Daven in a shul where they let a mechalel shabos b’ pharhesia daven for the amud?
Answer:
Although it is wrong to give the amud to somebody who violates Shabbos in public, it does not prohibit davening in the shul. Furthermore, it is even permitted to answer “amen” to his berachos, provided that he is not a kofer (does not dely the truth of Torah, the existence of G-d, and so on).
Sources: Iggros Moshe, Orach Chayim III:22.
