rationalfrummie and takahmamash:
The statements by various gedolim about YU are clear as to their opinion of the institution and its philosophy. It’s not “only” those particular Torah giants. Both Rav Shach and Rav Schwab, for examples, are (similarly) on record about this.
As to some gedolim refusing to enter the place while others did do so, different gedolim have different approaches to the same set of facts even while holding the same opinion on the matter.
To illustrate with a different example, the Chazon Ish and Brisker Rav both struggled greatly to defend the Jews in E”Y against Zionism. But while the Brisker Rav refused to meet, liHavdil, David Ben-Gurion, liHavdil, the Chazon Ish did meet with him.
So while their respective tactics were different, their daas Torah on the matter was otherwise the same and they fought these dangers together.