Hardly anyone thinks that open borders would destroy civilization,
Really? I consider it obvious for a sufficiently strong definition of "open boarders".
Also it wouldn't completely destroy civilization because the open boarders aspect would collapse before all of civilization did.
As per a recent comment this thread is meant to voice contrarian opinions, that is anything this community tends not to agree with. Thus I ask you to post your contrarian views and upvote anything you do not agree with based on personal beliefs. Spam and trolling still needs to be downvoted.