There is no justification whatsoever, Muslims said they were there to help oppressed and British says they are here to help oppressed again…for instance, Haider Ali and Sultan Tipu were considered savage who snatched the kingdom from a Hindu Raja…and later after defeating Sultan Tipu they let the son of maharaja be the Raja of Maisoor…irony…
Justified or no Brits ruled Sub-continent for 2 centuries…and to rule they have to killings…massacres are norm…
When there was uprising against Mohammad Bin Qasim, he ordered to burn villages along with villagers alive…to create impression and reduce the chances of uprising in future…Brits did same, Sultan Mehmood did same, i guess this the reason so few of Arabs, few of Ghaznavids and few of English ruled the subcontinent with huge population