would it have been better if.....

If man/womankind had never been outside the boundaries of their own nation, would the world be a better place?
Are boats more danderous than guns?
Are walls such a bad thing?
In a melancholy, reflective kind of mood, been studying the crusades and the slave trade, hence the questions.
Answers on a postcard please...persuade me that the world would be this bad even if Europeans had never made it off the continent.