I see both sides of this argument. However, my thoughts are thusly-Ny nephew is 6 and my niece is 6 months old, and yes, i see them ALOT.. and i mean ALOT.
If its an "Adult" function, your child needs to stay home. Period. Throwing a hissy because sweet little Jr wasn't invited is never adult, nor is it wise nor does it teach your child anything either. If the invite says Mr. & Mrs. Jones, that is who is invited, period, please don't call me up and ask if Jr can come. I'm uncomfortable, you are rude.
If its an Adult venue: ie high end (NOT FAMILY) restaurant, wine/cheese tasting, or a play in italian/french etc, opera, non-child friendly, why would you bring your child? They don't understand, they get bored and its not fair to the other patrons.
Finally, if your child is screaming or on a tantrum while your eating, shopping, on your cell phone, you may be used to it, but WE are not, its not fair to assume that the screeching howl that your child is doing is cute. Its NOT. Neither is allowing your child to reach over the booth, kick my seat or howl.