No, you didn't understand. The point is that you should follow things that make you feel good and cut off access to things that make you feel bad. Choose your experience. Curate your feed. That's supposed to be the whole point.
It's like the difference between enjoying a glass of fine wine and alcoholic abuse that causes cirrhosis.
This is more complicated than you suggest. One toxic element of social media is that it's difficult to really notice these subtle effects. It's only in aggregate that the "bad" is really recognizable. E.g., on a surface level, it may feel enjoyable to view happy people living the good life, while subtle jealousy and a sense of inferiority may develop over longer lengths of time.
So the counter-argument is that Instagram is not so depressing provided that one uses as little Instagram as possible ("curate, curate, curate")?
That kind of proves the parent's point (which wasn't that one can't possible ever find anything non-depressing/jealousy inducing on Instagram).