Well, Mohammed if he was a warmonger wasn't the only one. Like anything else, who knows what the effect would have been had he never existed? Rather like it's not altogether clear that removing Hitler would have changed much.
I'd quite like to have seen various ancient libraries survive for far longer than they did. Undoubtedly the loss of Greek knowledge in particular held back development of the Sciences for many hundreds of years. Take your pick from any one of the incidents on these pages:
http://en.wikipedia.org/wiki/List_of_destroyed_libraries
By the way, some -- most -- of these events are new to me, I was thinking initially of just the Library of Alexandria and the Chinese one, but all of those book-burnings in the Arab world caught me by surprise. (Well, four major library destructions in 500 years is perhaps not all that many really, but more than I'd thought.)