No open borders, there are always individuals who will deceive, manipulate and look only after themselves, and wouldn't stop at nothing.
Where kindness is, is hatred. Where open mindedness is, is traditionalism. You can't just assume that everyone is a good person, because the news show you every day, that this is not the case.
If we would live in a perfect world, where only sweetness and light excist, I would change my opinion, as long as we live in a world where people will murder others over their ideals or idology, I simply refuse the open-borders policy.
And everyone who thinks otherwise, excuse me, is blinded and naive, living in his own imaginary world. And I, for my part, rather live a safe live, than a free one.
Also borders are meant as a regulation of import and export, as for an example, there are some standards that have to be met to export to lands oversea from germany. To prevent the import of parasites.