Oh if religion wasn't responsible for "massive cultural destruction" then mankind would have invented something else to do it (whatever is meant by "massive cultural destruction").
I disagree. When you are absolutely sure that God itself is on your side, then there is no atrocity to big to commit. I feel that religious zeal has led to some of the worst catastrophes in human history. I would put para-religious zeal in that category too, like dogmatic forms of communism.
The Crusades and colonialism can’t be distilled down to single causes, but even if you tried, religious reasons would not be the main ones. Political and financial motivations were far bigger factors in both.