One of my cousins is a recent alumnus of ISI Kolkata and mentions that there have never been any complaints regarding ragging. 

Most essentially, there is a legitimate reason behind these institutions being different from many others. That being said, ISI, CMI, IISC, IMSC, TIFR, and HRI are mostly different from every institute because they are primarily research-oriented. The list also incorporates IIT, NIT, BITS, IISER, NISER. These institutions are completely free of the Students Unions Ragging, students clubs, and more.