I think it’s the filtering out of pulp and other solids, leaving only sugary juice that would make it unhealthy. However the point of a smoothy is to blend actual fruit including fiber and other solids, and throw in some protein

Veggie smoothies would be even more healthy than fruit smoothies but I’m not up for trying that yet

My blender has a “Smoothie” program with varying speed and pulsing and sensing when it’s done, so it’s literally one click