1) IANAL, but there are circumstances and legal jurisdictions where truth is not necessarily an ironclad defense against defamation claims.

2) Ironically, I think the stronger the defamation laws, the worse the problem of defamation becomes because more people become likely to believe dumb random claims they hear are true or otherwise nobody would risk saying it. I believe that a hypothetical society with no defamation laws would be the safest from people believing false random claims.