You are not serious?
The practicalities relate to recruiting a suitable number of identical twins, to getting consent (they would be minors), persuading them to adopt lifestyles that are fundamentally different, monitoring their compliance and following them for a very long time. Enormously expensive for a start.
Ethically the other problem, other than consent, would be in persuading someone to wear a bra if you thought it was unnecessary or harmful. Someone with no views on this would need to do it, if they were allowed to, which I doubt.
(One of my jobs is research administration).