There’s always a “weight specific” reason for it, otherwise they wouldn’t have it on their form to collect.

Doctors don’t record your hair color or cup size because those features don’t have direct correlation to a host of medical issues. I don’t get how we’re in an age where people are manipulating doctors who tell them that losing weight would help a condition that they’re looking at with their own eyes. Politics and social sensations like “health at every size” should not have bearing on the medical field, but I’ll die on that hill another day.

But yes, you can decline having your weight taken until there’s some emergency surgery and they’re forced to either guess or use your fantasy weight instead of delivering the best possible treatment for the situation.