They(Muslims) get angry if you tell them that they used to be Hindus. Whatever they used to be before they converted to Islam is supposed to be "napaak"(impure/unholy) and they are not supposed to even talk about their pre-Islamic past. According to them, their past is supposed to be "uncivilised, shameful and satanic". With the acceptance of Islam they have now become "civilised humanbeings". Their past is supposed to be erased from their collective memory and should leave no trace of their previous culture , belief or lifestyle whatsoever. For them, their history begins only after the birth or conquest of Islam. Events before that are given only a passing mention.
Then they're hopeless. There's just going to have to be a major war; the earth needs to be rid of Islam.