I feel very strongly that women should feel uninhibted to nurse whenever and wherever they like. Our puritanical culture inherantly looks down upon anything that might involve the removal of clothing in public, which is great for preventing the exposure of pornographic images to young impressionable minds, but terrible in light of the fact that less than 30% of mothers nurse their children through the first six months.
Of course being discrete is a courtesy nursing mothers should consider extending to others, but I for one would rather nurse in the chapel than pack everything up and step all over people trying to get out of the pew, disrupting the service as I drag a screaming infant across the chapel and out the doors. It's easy to be discrete (I use a "hooter hider"--$8 at Target), and most people don't even notice. The nursing lounge is great, but women shouldn't feel like they're "banished" there to feed their babies. If she wants to stay put, I say let her and bravo for nursing her baby
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ETA: If those missionaries were disturbed by a mother discretely and modestly nursing her baby during sacrament meeting, they should thank their lucky stars they didn't get sent to any South American missions
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