yes, all sorts of things can backfire, which is why you should think about them carefully, and after a thoughtful, careful analysis, decide if you think the potential rewards outweigh the risks.
to me, this idea of thinking things through first is second nature -- i've been doing it all day every day for prob 30 years -- as any would-be activist should, imo.
and that comes with a realization that the lives/careers of some people may and will be harmed in almost any policy you advocate for -- and that's not a reason to _not_ do something -- because doing this analysis and advocating for anything or just doing anything that has consequences is part of growing up and being an adult.
so, going to war against hitler and the axis?
very bad for myriad soldiers on all sides (wounded, killed, etc.), very bad for nazis (except all the ones we/US rescued and rewarded and used for later terror campaigns), very bad for most of the citizens of Hiroshima and Nagasaki and countless civilian victims the world over, but very good for Jewish people in Europe and myriad groups of dissidents/disabled folks/gays/etc., very good for western-style democracy -- so, on the whole prob still good for the world -- it was the right thing to do, imo -- to go to war against the axis, even if, in the end, the US population had to be largely tricked and otherwise dragged into it, and the US elites mainly did it to stave off the threat of being conquered by the Nazi/axis elites.
i suspect, given the precariousness of work already, a 4-day work week would probably increase workers' economic stability -- but need to study it more, and would need to continue to study it even after efforts began.
if/since companies have not strongly resisted the 4-day yet -- it makes me think they see some distinct advantages in it, which is worrying.