I don't think anyone hates UP, the institution ... more likely, they just hate some UP personalities for varied reasons (mayabang, egotistic, feeling superior, presumptuous, etc.), in other words personality-based, either bred by the institution or their peers. It is hardly social polarity because UP prides itself with having students and alumni covering the entire economic spectrum. Neither is it because they did not pass the UPCAT nor because of non-payment of taxes as these are presumptively arrogant issues that have nothing to do with their hate.
Whether good or bad, UP is unique, a sui generis, you either hate it or you love it ..... parang si Jaworski lang! 🙂