If ten of us were to chip in to rent a billboard, there'd be sales tax on the rental, but our "kitty" would not have to pay income tax on the money as we chipped in, it would have been previously taxed  as our individual income. Similar to Campaigns being exempt from tax on the donations they receive.

Tax deductable orgs are subject to strict rules limiting their political spending, tax exempts are not. But they still have to comply with reporting rules when they spend.