In what way would they ban something? I mean, what would that mechanism look like? Honest question. It seems that they would only be able to rule some legislation unconstitutional or to rule on a case to set a precedent.

FWIW I think the Supreme Court overall does an amazing job upholding the constitution. The Roe v Wade upset made sense from a legal perspective and they have a strong recent history of supporting citizens rights in the face of overreaching LE agencies.