if BA decide not to operate their own dedicated freighters and out-source to someone else then it's free for the taking surely.
BA are free to do lots of things. For the sake of industrial harmony they tend to consult with the BACC when it comes to matters regarding pilots. The compromise that was reached when BA decided to outsource the flying of much of it's cargo was the secondee agreement. That agreement is no more/less disgraceful than GSS pilots choosing to fly BA cargo at a lower rate than BA pilots.
We all live in the real world - I harbour no ill will against any GSS pilots, however I've got no time for anyone who would take issue with me should I bid for a GSS secondment.