I think that if the vote is legal then strikes, while generally undesirable, should be allowed to proceed. The strikers shouldn't be allowed to intimidate those who choose to work however, and I can't see why anyone else should be coming out in sympathy.
This particular case strike seems mental to me, and the Unite leadership are particularily disagreeable and with an agenda above and beyond the needs of their membership. It seems clear that BA need to do something to compete, and while I can see there are leadership failings in the company, reducing cabin staffing to levels already prevalent in the industry doesn't seem like an unreasonable step.
I was slightly surprised to hear the Labour leadership calling the strike deplorable – they might not like it or agree with it but that's too strong a term for something that's entirely legal. It's the sort of language you might have expected from the Tories, but shows how far Labour have strayed.