Why the hell does anyone bother with sanctions on Iran?

I do not understand why anyone is advocating placing sanctions on Iran. The regime is hell bent on ignoring them. The population by large margins supports the use of nuclear technology. Sanctions have the effect of bolstering the popularity of the regime. Is this a game as a pretext to later bomb Iran? By using sanctions when they are quite clearly impotent one devalues their importance. It also makes the average Iranian suffer enormously. So why is it morally acceptable to impose sanctions?