In a teshuva written in 1953, Rav Moshe Feinstein responded to a question by Rav Naftali Carlebach of Detroit as to whether one could invite people to a minyan on Shabbat if it was known that they would travel by car. Rav Moshe responds that despite the kiruv aspect, it is definitely forbidden, not only because of לפני עור, but also because of a conceptual relationship to the notion of מסית. Rav Moshe then says that if the people in question live within walking distance but may drive anyway, then there is still a לפני עור problem but not necessarily one of מסית. Furthermore, if there is no explicit invitation to join the minyan, merely an informing that the minyan is going on, then it is questionable if there is any problem.
In the final paragraph, Rav Moshe deals with the question of whether or not someone should quit a shul where many people behave improperly. Rav Moshe feels that one should remain in such a shul in the hopes of being a positive influence, and should not despair. However, if the shul is actively regressing, such as by removing the mechitza, then a person should certainly refuse to be a member of such as shul.