Well if you believe this thread was a response to the thread you are talking about, then fine.
But if it is a response to a real-life incident, as the OP says, then you can see that more than one woman who is not suffering from infertility has seen fit to opine on how secondary infertility is worse because women who can't have any children don't know what they're missing. 
I don't think it is hard to see how maddening it must be to have your situation minimised in that way.
In the same way that someone who has not suffered a still-birth can't claim to fully understand that pain, a woman who has children can only imagine (or remember, from a place of knowing it all worked out) the pain of unchosen childlessness.
It is a nonsense to weigh the loss of babies up against one another. I would never, and have not, said that anyone should be doing that.
But I would be more than a little
if someone who had suffered one mmc and had gone on to have a successful pregnancy insisted that her loss, her pain was the same as that of someone who had lost a baby at term. Or worse, claimed it was better to have a stillbirth, because at least you got the whole pregnancy.
The OP didn't suggest that multiple losses and stillbirth were what she was talking about. Like you say, that is a separate issue. If she had expressed (or anyone had) impatience with women who have children talking about the pain of multiple losses, it would be a different thread. A much shorter one.
There are people who think it should not be allowable to discuss the fact that primary infertility is its own special pain. That are insisting that we must all accept that the pain of infertility is the same, no matter what your history of having children.
I think that is a massive liberty.