One wonders if the British were even half decent when you consider their long history of colonial and imperial oppression. One might conclude they were fully indecent, in fact.
Do you think it's strange that some of the HK protestors have been waving the flag of their former colonial masters?
Amritsar caused outrage in Britain and changed the whole narrative. It took time, but within a decade British government had lost all moral ground and British attitudes had shifted.
As evil/bad as the situation was; non-violence only helps if someone loses more than they gain by just killing you. In this case it was by losing the moral high-ground that was valued by some British people at least. Sure it probably wasn't decent people among the perpetrators, but the pearl clutchers back home.