Agreed. My eldest was about 6 weeks old when my best friend from childhood days was married. He was matching the soloist who was beautifully singing "Ave Maria" when I had had enough of trying to cuddle and rock and said WTH and pulled up my sweater as my husband handed me a blankie.
My mom went into catatonic shock when I related this tale to her. "Well! You should have left!" I retorted in my charactaristic sweet fashion that weddings and funerals that are attended by babies are God's best reminder that life ain't perfect but babies are.
I think it's less disruptive just to nurse the baby, unless he won't do it quietly, than to get up and leave a function. Of course, the really little ones often have diaper disasters right after eating, so it's a judgment call ...