Why might insiders be able to cause damage to their organizations more easily than others?

Yes, it is true that people working inside the organizations can cause more damage to their organisations than any other person. Insiders have all the information of that organization regarding their actual performance, financial standings, product portfolios, current and future plans, goals and strategies. They know the exact reality regarding the organization that where it is heading and where it want to reach in the future. What action they might be taking for to achieve their future goals. If they do not work in the right direction, or they leak out that information outside to someone else, it might pose a big harm to that organisation and the consequences could be very horrible for the organisation.