50% Reservation in premier institutes like IITs and IIMs. Apart from the damage it does to the repute and quality of the institutes and the lower half of the class, there is a bigger danger for the other 50% also.
The intense competition to squeeze in one of this institute will glorify the entrance exam so much as to demand unrealistic efforts from the students. It will create a big burn out risk as getting into these institutes would become the success rather than way to success. This burn out will affect the quality of the institutes which are already concerned by the coaching class generation and trying for reforms in exams to limit the coaching institutes.
But such an vote bank appeasement action will lead to higher and more intense competition and hence greater reliance to coaching classes. And once a student comes through, he would be delighted and on cloud 9. He might be so frustrated by investing 2-3 yrs of his life into the jee/cat so that he might not feel to study anymore once in there and his motivation to study will be affected. Hence in effect we screwed up the bottom 50% and the top 50% is burnt out! What do we expect now?