Complex sentence: Aside from the complaint that pushing for mass conversion of non-Muslims to a different religion and culture is intolerant of their beliefs and aggressive, Olivier Roy argues it is simply unrealistic in an era where religious belief is considered a personal matter.
Split into simpler sentences: Aside from the complaint that pushing for mass conversion of non-Muslims to a different religion and culture is intolerant and aggressive, Olivier Roy argues it is simply unrealistic. "(T) he age of converting entire peoples is past," as we live in an era where religious belief is considered a personal matter.