Not to defend the manifesto or it's content:
1) It's all to common for people to reinterpret a claim of the form "biology has significant effects on the behavior of humans in the aggregate" into "we can assume biology is a limiting factor on individuals". Since the latter is an indefensible position this technique is used to preemptively invalidate any argument that actually only claims the former. This is what you've just done here, intentionally or not and it's an unacceptable intellectual dishonesty.
2) You're also dramatically misattributing the attempt to determine "what ought to be" to only one side of the argument. One of the article's key points is that the pro-diversity advocates take it for granted that "what ought to be" in the world of tech employment is a 50/50 split between the genders based on the biological basis of sex-at-birth ratios. The truth is that the natural, not unjustly-influenced equilibrium is not known to anyone on any side. Choosing any specific ratio (even 50/50) necessarily implies defining what the genders are or should be. (Including how many genders there are and which ones you accept!) For example, saying that the ratio should be 50/50 is to say that in this respect
women should not differ from men, even by their own choices.