Depends on your attitude to your chosen profession. Balpa is not perfect, by any means. But they are engaged in every aspect of your career at many levels in an endeavour to act on the concerns of their members and on behalf of this fine profession. By becoming a member and supporting them and perhaps taking an active part in such proceedings you can be a part of this process. Otherwise, like some, don't bother, save your 1 %, and just whinge on the sidelines about pay whilst accepting the benefits that are brought about by the contributions of your colleagues.
Like I said, it's not perfect, but the choice is yours - do you care about your profession or not ?