Safety Concerns:
I have no personal problem with staff travel being withdrawn from striking workers. If it had been a contractual benefit my opinion would be different, but it is not contractual.
If BA loses any legal engagement and must return and/or compensate those individuals who have had their staff travel withdrawn then so be it.
However, at the moment, and I don't see this changing, BA is capable of and has withdrawn this perk.
As for "Unite has filed..." to be the best of my knowledge and belief Unite hasn't filed anything anywhere. The basis of your argument seems to be "It isn't fair, going on strike is legal...so it isn't fair".
Until such time as a governing body says "No" I would submit to you that it is fair, its just a result that a few individuals don't like.