I have no problem with going on a legal, well planned and well advertised strike as it gives customers a chance to plan and book with other airlines.
There simply is not the spare capacity in the market to allow even the majority of your customers the opportunity to travel with another operator. In some cases at your 'regional' bases, there is no feasible alternative to get to the destination intended, without travelling some distance. Even if there is spare capacity, many customers will be priced out of the market due to the sudden high demand. Ryanair could well be the exception to this rule though, from a
PR point of view!
Be under no illusion that any industrial action that takes place on such a large scale, will leave the customer with just as many options as if your groundstaff were indeed.....
Telling them at the gate that their flight is cancelled.