MARJAH, Afghanistan — The Taliban’s white flag no longer flies over villages across this militant stronghold. Afghan and NATO troops have replaced it with Afghanistan’s official green-and-red banner, which they promise heralds new schools and clinics and good governance. But residents have heard that before, and for many, Taliban rule hasn’t been all that bad. Plenty of Afghans have made a living off the opium trade, which also funds the insurgency. While some residents greet NATO forces with tea, others just want the troops to clear their streets of explosives and leave.