Why is “get more women into STEM” a worthy goal in and of itself?

Well, it depends on whether women stay out of STEM because they don't care about programming, or whether they stay out of STEM because they're worried about being alone in a toxic environment. Ideally a diversity program would not influence group 1 while solving the problem for group 2.

That’s a different problem. “Fix toxic environments that keep certain types of people out of an honest line of work” is a good problem to solve. That is not the same as “let’s increase the number of people of a certain demographic within an industry”, in and of itself, taken entirely on its own.

If you phrase the problem like that, there is no problem. Group 1 is tiny compared to group 2.

I think addressing group 2 is a desirable and valid goal.

Societal gender roles say nurses and teachers are women's work and STEM is man's work. That's the thing one would need to address, and at a young age. It's not entirely clear how one can do that. One "only" has to challenge the societal norms that define gender roles themselves. Not an easy problem.

>Group 1 is tiny compared to group 2.

That is in my opinion an unjustified assumption. Huge numbers of men and women are uninterested in programming. In fact, virtually everyone I know of either gender is uninterested in programming. The number of people who don't program because they're not interested anecdotally dwarfs the number of people who don't program for any other reason.

I got the two groups mixed up. Just swap 1 for 2 in my comment, which I can't edit anymore. I fully agree with you.