The "healthy at any size" kick isn't talking about an extra 20 pounds. From the pictures I've seen it is at least an extra 100lbs. The problem is by removing the stigma of being obese, we are ushering in massive health issues and disease for this upcoming generation.
Shockingly, it turns out if you tell someone with 100 lbs to lose that they are a disgusting lazy piece of shit doomed to an early grave, they tend to withdraw from health care and other social settings, seek comfort in unhealthy habits, and suffer from anxiety and depression. They may give up on their health entirely. After all, if you've struggled your entire life to lose weight and made little progress, then what's the point?