One to one isn't an arbitrary ratio, though; it's the ratio of women to men. There are questions about positive discrimination, but I feel I have to point that out.
One to one is, however, not currently the ratio of women to men who are qualified as programmers. This implies that less qualified women will have to be hired at the expense of qualified men, in the world as it is now.
Shifting towards a 1:1 ratio would be nice, but that needs to be fixed by growing the talent pool, and isn't going to be solved at the hiring practice level.
It's arbitrary in the sense that 1:1 implies meaningful equality. Forcing women and men to go in and out of fields they like simply to enforce numbers is not equality, at least in my sense of the word.
To me, giving women and men a fair and equal chance at working in X industry, is equality. We have no idea what that ratio would be though, but i highly doubt it would end up at 1:1.
Shifting towards a 1:1 ratio would be nice, but that needs to be fixed by growing the talent pool, and isn't going to be solved at the hiring practice level.