The way it was sounding, it seemed that what Anne was trying to say was
that just because this couple didn't want the OP's baby at the wedding,
that must mean they weren't really her friends. I don't know whether that
was really how it was meant, but it seemed well over the top to conclude
that purely from the couple wanting their wedding to be child-free.

no that wasn't what it meant at all, what I meant was that a true friend
would understand why you couldn't come, which would either mean they changed
there decision about the invite, they may just plain have not understood
what it meant to be a breastfeeding mum, or they would regretfully explain
there decision and express there sorrow the new parents would not be there,
but also there understanding as to why that was so.

There is usually some room for manouvere with wedding invites, we had to
make some changes. Naturally we invited cousins, it turned out than one of
my cousins had a serious girlfriend we weren't aware of, should he have kept
quiet and not mentioned it? I don't think so, I'm glad that Rachel was
there, even if it was the first time I met her, but they were engaged
shortly afterwards and are now married. Similarly we invited a friend who is
disabled, his condition varies and at the time of the invite we'd not
expected him to need assistance, he delayed in replying not knowing what to
do, thankfully we realised and extended the invite, they responded with a
very generous gift.

Which is better, to respond formally and politely in the negative, or to
have a friendly chat, expecting nothing, but at least keeping communication
channels open?

Anne