There is a lot of politics wrapped up in this and it is a contentious issue online, but certainly a central part of the issue focuses on the role of Churchill during the Bengal Famine. A few past answers look at this from various perspectives including this one from /u/LordBigButts, this one from /u/abrytan, and this one from /u/Naugrith. Each takes a somewhat different approach, but certainly all help illustrate the underlying issues that lead to such a strong dislike (hatred, even?) of Churchill in large swathes of Indian cultural memory.