Fidget items can have practical uses that help people calm down and stay focused. The problem with spinners may be that they require visual attention, which can distract users and others nearby.
Baseless claims about the damage done to kids' development create needless panic. And they distract from legitimate, evidence-based concerns with which parents need to engage.
Aren't there huge health benefits to staying physically active, for adults? Why should it be any different for children?