The problem is that the imbalance is what's discouraging women from entering STEM careers; addressing it just means doing things like this conference is doing to increase female participation.
But to say an entire sex should do something is nonsensical. It's entirely possible they don't want to study stem.
You realize these two sentences contradict each other, I hope. You say that it's non-sensical to discuss what the entire sex should do, then try to talk about what the entire gender may or may not want as a reason for (or against) acting.
To say that they're under-represented is to belittle what individuals choose to do with their lives.
No, it doesn't, because it doesn't require any individual to do anything, or to give an individual responsibility for what the entire gender does.
When I talk about "under" represented, I mean that absent the historical injustice of sexism, you would see a different gender balance. And as this conference and GoGaRuCo demonstrate, when you control for the historical imbalance, women and men are selected equally to speak in a blind process, thus showing equal ability, if not interest; it's reasonable to assume that after correcting the historical artifact, gendered participation ratios would be much closer.
I've already agreed that affirmative action isn't the answer, but this--community outreach, basically--isn't affirmative action in any sense.