As I posted on another thread yesterday -
TGWU is now called Unite after merging with several others, read it on their website or wiki.
I have long been an advocate of BALPA getting under the folds of Unite but, until that happens, I think that Unite would direct you to BALPA if you wished to join, my info may be out of date so don't take my word on it.
I don't think it has anything to do with socio-economic groups, we all have aspirations, but had more to do with that union considering that you would be better represented elsewhere, the world of aviation is a very specialised field.
However, now that BASSA is a section within Unite and they represent CC outside of BA they may be up for accommodating pilots, you would have to ask. I am a total outsider in this but a long standing union person and would take the view that the old dog has to be very sick before you make the decision to put it down. if it is not then the only medication can be an input of members who are willing to become active rather than passively demand. That includes asking how your money is spent and especially focussing on how you deliver protection and representation to members. Perhaps Unite has greater experience in that delivery and perhaps BALPA could ask them for assistance, it is not unknown.
You may respond to this post by flaming me or agreeing, I would prefer that you do this within YOUR union.
Edited to add - I do not consider the IPA to be a realistic alternative.