[Tantumergo]

"I would however like to know what reason is there to ignore the natural reading of brother = literal brother."

Because until very recently, all Christians believed that Mary was perpetually virgin. Therefore the Scripture was interpreted in the light of this common, ancient belief and thus "brother" was never understood in its literal physical sense.

Luther, Calvin and Zwingli all believed and defended her perpetual virginity, and this doctrine was never part of the original Catholic vs. Protestant controversy. It was something that all were agreed on.

That it has become an issue in more recent times is probably due to the way the English language has developed over the last few hundred years. Words change their force, meaning, and latitude of interpretation over time. e.g. what do the words "gay" and "wicked" mean in colloquial speech now compared to 100 years ago?

[UsnDadof8]

Because until very recently, all Christians believed that Mary was perpetually virgin.

Right. Yeah. Okay.

First of all your premise is wrong. But even if we assume it to be right, what you're saying is that we should let our opinions overrule the plain assertions of scripture.

[redgolum]

The perpetual virginity of Mary has historically been a Lutheran view, but it wasn't ever a "dogma", since the Bible is a bit ambiguous about it (hence why we are having this discussion).

While many Lutheran bodies don't touch on Mary that much, we still have a feast day for the birth of Mary (just recently) and treat her with a lot of respect as the most blessed woman in history.

After Vatican I in 1870, most Lutheran churches began to tone down any overt mention of Mary in the liturgy.