The Muslim invaders raped so many European women and killed so many European men as they blitzed across the Mediterranean world that the population went from looking like Romans to looking like Arabs
And even if they didn't tax churches, they abducted Christian boys and raped them, or turned them into janissaries, as shown by the twin tales of Skanderbeg and his brother
This is why Martel and the Franks were heroic for stopping them at Tours, the Hospitallers were heroic for stopping them at Malta, and the Poles were heroic for saving Vienna
Muslim invasion brought with it the same problems as Muslim migration, which is the horrific rape, abuse, and murder of Christians