they aren't /designed/ to do that, but might do so anyway - the post implied it was a foregone conclusion and your example simply states it as a possibility. I'll say that it is corporate interests - not unionized worker interests - that are dominant 99% of the time. And if a union were to strike - successfully - against some automation it would be a matter of time before corporate interests would get politicians to re-craft laws, they'd move to another state (or off shore) or whatever.
I worked a non-union job that was automated away and no union struck for me, and it would not have made much difference if they did.
in the IT world much of what we do is essentially managing systems that would have employed dozens if not hundreds (or thousands) and now can be done by a few or none. Much of what I do now can be automated and frankly it's so deadly dull I'd be happy to see it go (if only those pesky business interests could come into play now).
you failed to mention if this Longshore strike was successful, merely that it happened. I'd say that's on par with Republican anti-gay marriage laws - purely symbolic and destined for defeat.
Unions can and do protest anything they like, but their primary goal is collective bargaining and worker representation, not dictating how a business operates (it may protest as a form of free speech, just as any person may do so, and, uh, more power to them, right?) unless it's directly vis-a-vis worker treatment just as you might hire a lawyer to represent your personal interests.
If your contract says you are guaranteed a job for year and they fire you after a month and say "oh yeah, we replaced you with 5 perl scripts" you might protest with your union-of-one - a laywer who represents your /personal/ bargaining interests. That's not "being against automation" that's representing your contractural rights.
If I was in a coma since the 1950s it's because unions are gone, and this was accelerated during the Reagan years and the middle class demolishing policies of Republicans under the banner of subsidizing the rich disguised as being "pro business". Wake me up when the unions are back m'kay?