A Post business columnist and an independent music non-profit have joined the chorus questioning Live Nation’s proposal for a Silver Spring music hall. Last Friday, Steven Pearlstein wrote that while I.M.P. boss Seth Hurwitz has fought against competition for his 9:30 Club before, and his alternative proposal to Live Nation is in his own best interest, “he’s put forward a financial proposal attractive enough that county officials cannot ignore it.” Under their non-binding letter of…