Litebulbs
Your point about some people wanting to empower centralised control could easily be negated by Unite allowing a ballot on the deal, or indeed holding a ballot themselves over the heads of the BASSA and CC89 committees. What could be more democratic than allowing the members themselves to decide whether to accept the deal or reject it?
The members would then be responsible for the result, and their union officers for dealing with that result. What are Unite afraid of? Clearly they want rid of this dispute, but if the members as a whole are committed to carrying on, so be it.
Much like any professional advisor that you may employ, the union officials can only advise what the ramifications are of any course of action and deal with the outcome.
If your Doctor advises you not to skateboard on the motorway, but you insist on doing it, the Doctor is morally obliged to treat your injuries. Likewise, whilst taking union dues off workers the union are obliged to represent their members whether they believe in the action or not.