It's a BS argument. A lot less than 50% of programmers are women, so there is no way 50% of open source projects (as a sign of merit, as I understand you) could be started by women.
Obviously, women do want to be programmers, unless they are told by society that they shouldn't or couldn't. If that weren't the case, movements like DjangoGirls would be far less successful.
The comparison with fashion design is also BS. For one thing, there are lots of male designers (especially the famous ones) and then the number of fashion designers is a lot lower than the number of programmers.
And this is not as irrelevant a choice as whether to play with dolls or lego: Programming is a skill which allows for social upwards mobility like nothing else. Just assuming women (and minorities) don't want that, is a bit too easy.
There is nothing to "solve" here. Let people do what they want to do.