Even those that accepted it did so in a restrained manner. The Mir in Europe had a 40 min and a 45 min session each day. The Mir in NY had 20 min and 15 min. Nothing like what Reb Israel Salanter was contemplating.
Reb Chaim Soloveitchik did not allow Musar in his Beit Midrash. And in my first yeshiva of Reb Shelomo Freifeld it was absent. Many Litvak's considered it a distraction from Gemara.
My own learning partner said to me he is "allergic to Musar."
This is a difficult subject because my own experiences with Musar have been varied. At one point I was all 工合 gung ho about it.
My impression is that it is like vitamins. One can overdose. But one can underdone also and have MDS (Musar deficiency syndrome).
I have seen plenty of people with MDS. And it is chronic. It can get so bad that even a small amount of healthy Musar can cause an allergic reaction. Yet there are plenty of people who have over dosed also. It is hard to find the middle of the road. What tends to put off people I think is the "mashgichim" that make Musar into a business. They are not smart enough to be Rosh Yeshivas yet they are somehow connected by family relations, so they are made into a "Mashgiach." It is hard to find a better group to give Musar a bad name. They are the terror of every yeshiva bachur- student.