Why does watching my work get twisted wear me down?

You did careful work. Then you watched someone twist it to fit their argument, or worse, watched no one notice it at all. That is a real injury, and the hope that first drew you to this field is leaking out of it. Name that plainly — don't dress it up as cynicism or call it maturity. Here is what you have confused: the making of the work, and the fate of the work. The first was always in your power — your method, your honesty, your care. The second never was. You cannot control who reads it, who misquotes it, who uses it as a weapon. You have been grading yourself on an exam you were never given the questions to. If the erosion has gone past frustration and into something heavier — if you no longer want to get up and do the work at all — that's worth saying out loud to someone who knows you, not just working through alone.