Code Access Security is a joke?

I have just read about this article about Code Access Security. It has such an example in it:

using System.Security.Permissions;
public class MyFileAccessor 
{
  public MyFileAccessor(String path, bool readOnly)
  {
    path = MakeFullPath(path); // helper fcn
    FileIOPermissionAccess desiredAccess = readOnly
      ? FileIOPermissionAccess.Read
      : FileIOPermissionAccess.AllAccess;
    FileIOPermission p = new FileIOPermission(desiredAccess, path);
    p.Demand();
    // 
    ••• 
    open the file
   }
   // •••
}

What if I didn't use the FileIOPermissionAccess type and never includ code like p.Demand() in my code at all? In other words, if I want to do something bad, why should I bother to ask permission for that? Isn't it kind of a joke? OR did I take it wrong?