Is it really BALPA who are threatening you.
No Fred it isn't BALPA: it is a BALPA member writing on behalf of other BALPA members who made the threat making allegations of secret BALPA lists to persecute individuals who disagree with them.
Frankly, it is rather childish: a sensible debate on the pro's and cons is what is needed not the personal attacks and threats from BALPA members because we don't agree with them.