When people go and talk to women who started out in the tech pipeline but left, many say that the reasons they left are that they felt unwelcome in some way: they were harassed, under-valued, talked over, stalked, underpaid, etc.

Too many women choose to leave not because they didn't like the work, but because they didn't like all the bullshit they were implicitly asked to put up with, in order to do the work.

If very few women expressed these sentiments; if the tech workforce pipeline was a safe and fulfilling place for everyone, then at that point, I think it's fair to question whether 50/50 should be the goal. But we're not nearly at that point, and IMO it is counterproductive to talk like we are. For now, the numbers imbalance is a simple and obvious way to measure and talk about the cultural factors that exclude women (or certain ethnicities, or backgrounds) from equal participation in this industry.

One reason 50/50 makes a fine straw goal is that there is no obvious reason that men should be more successful than women in the tech industry. It's not like the NFL, where well-understood human sexual dimorphism is relevant. Women were heavily involved in the early days of computing and built some of the early foundations of the field, like the first compiler.