Not to put too fine a “pint” on it, what “horrible attrocities” has the Church of Rome committed that were worse than those committed by Protestants? In the religious wars in France and later in Germany, both sides acted with savagery. In England, the government of Elizabeth persecuted both Puritans and Papists with zeal, but killed as many Papists as Mary killed Protestants. Oliver Cromwell was as savage in his suppression of the Catholic uprising in Ireland as the Inquisition had been in the Netherlands.
If you are looking only as far back as 'Protestants', you need to have another look. You are missing more than half of the Roman church's escapades.
As to whose atrocities were whose, who am I to judge between the whore and her daughters? But then, one must suppose they only knew what their mother had been teaching them for a very, very long time... So maybe that might help to affix blame.