I had never thought about it that way...but what you're saying makes sense: that some people who wield the phrase "Life isn't fair!" are actually trying to repurpose it as a motivator. To challenge their conversation partner to actually take action rather than just whine and gripe about the problem. I guess having been subjected to too much Jessica Wildfire tends to make me jaded.

Still, I do stand behind my original premise: it isn't my job to read somebody else's mind. So if someone says "Life isn't fair" and they're intending to inspire the other person, then they'd better back it up with an actionable sentiment. E.G., "Of course polluters aren't going to listen to you; life isn't fair! So what are *YOU* going to do, individually, to help move the needle on climate change and inspire others to follow your lead?"

Contrast this with, "Life isn't fair; we're all fucked!" (assuming that the "We're all fucked" part is silent and implicit, since the person ended their dialogue with "Life isn't fair").