thoughts on "healthy at every size"

Only to a point. Excess body weight puts stress on bones and organs, can also cause diabetes and other health issues.

Trust the science, after all they tell us that the morbidly obese are healthy, men can get pregnant and the clot shot is good.

after a point .. not really

every body type has a "health envelope" the shape that is best for their bones, heart, height etc.
but too skinny is unhealthy and too fat is unhealthy.

that said most shgapes can look very nice at either end of the healthy spectrum

The resting heart works best at 50-80 beats per minute.
Anything above that means your heart will work itself too hard.