Phantom Driver, well said and spot on
One of the hardest tasks for airline pilots is managing risk. What makes it so hard is that we have to put our big egos aside and look at it from a safety standpoint. This is especially crucial in todays world of FDAP and other flight deck data recording programs.
Circling approaches are like engine failures. We practice them in the sim, and should be able to handle them well enough. But, if landing at our destination meant flying a one engine inop approach and our alternate meant landing with all engines - no sensible pilot should continue on to the destination.
There is just too much risk involved in flying a circle in low weather. We've all heard about good landings being preceded by stable approaches. Well, a circle is anything but a stable approach. It is something we do very infrequently, therefore it is very hard to keep it stable. Not to mention that you will most likely be flying manually while trying to keep visual with the airport, often taking configuration changes at non-standard times. Today's airline procedures and cockpits are just not designed to be "circle friendly".
An airliner has no business flying a circling approach in IFR conditions. Circling should be a visual maneuver restricted to high VFR minimums. Yes, a professional pilot should be able to fly a circling approach, but you should stay ahead of the airplane so as to prevent getting yourself into a situation where you have to circle in anger.