They think this is acceptable because the countries they idolize do this. USA and UK committed many horrible crimes across the world, but still talk like they are saviors of humanity and tries to constantly remind the world of this. The US and UK has therefore given little exposure to India, it kinda reminds it of itself mask off without pretentious notions of moral integrity and without any real world power, just hate and needing to murder other peoples in order to keep their own people from doing it among themselves but no ability to do so.
When it comes to the Europeans, it was comitting evil for conquest. They didn't always enjoy it. Evil for conquest and maintaining status. The Chinese have been looted, raped and pillaged throughout history (the first victims of the Mongols) and we are this way because we are not very combative or good at being combative. Chinese especially southerners are generally too soft, weak, and magnanimous when it comes to these things. We're good at counting and saving pennies but totally pound foolish. All that's built up will be destroyed by those who are combative and naturally better at it. Since the Mongols took over, things have become a little more different but to get back on point, Indians commit these evils and dream about doing it as some form of proof to themselves that they are "worthy".
They don't do it for conquest or material gains like the Europeans, they are motivated by their inferiority complex and deep trauma at centuries of bloody rule by the British and millennia of rule by Muslims. They have something to prove to themselves and the world. Which explains why Indians are super sensitive about their progress and take much effort at slandering others like China, a nation who was where they were 100 years ago and have long since left them in the sewers.