I don’t think at ND the Catholicism is shoved down the students’ throat. The Catholic spirit is there but is not forced. They even have Moslem students association there.
When we went on a tour, one tour guide joked that during application process, 80% were Catholics, but once they were admitted, the numbers dropped to 60%. Another guide mentioned that he (a senior) only went to mass once during his 4 years there. There are daily masses in each dorm but students are not required to attend.
Yes, ND doesn’t offer sororities and fraternities. So if that’s your main factor, then ND is definitely a NO.
Northwestern and Notre Dame are also very different location-wise so I suggest you take into account this factor. Compare how you feel with the Chapel Hill area.