In this context, it means "easy to enable, but if the child process does not handle errors correctly, it might be confused by all the pledge violation errors it

In this context, it means "easy to enable, but if the child process does not handle errors correctly, it might be confused by all the pledge violation errors it gets for syscalls that used to always work". This is a bit unfortunate, and requires a implementor to apply a bit of elbow grease. It specifically does not mean "hard to get right so that the intended security level is achieved". Such a scenario would be problematic.