<<The group that had butter either belong ... to an old fashioned rural
group, often farmers. And it is known that kids that grow up on farms have
less allergies.>>


Ah!  So the reduced incidence of allergies may have something to do with a
"farm lifestyle", in which eating butter is one of many factors.

I don't question that butter is healthier than margarine.  I've just learned
to question the generalisability of epidemiological studies, especially as
the media frequently mistake epidemiological associations for cause and
effect.

Rob