Appeals to literalism or objectivity often serve to create a seemingly objective and seemingly simple veneer over something that's truly subjective and complex.
In this case, "women are baby machines" is obscuring a lot:
- This is conflating being female with being a woman. Being female is a biological fact, being a woman is a distinct concept from being female. Conflating them serves to imply that our ideas about womanhood are objective rather than constructed. But most of our ideas about women have nothing to do with any biological reality - there's nothing about having two X chromosomes that means you wear dresses or engage in girltalk.
- Many women can't have children. However, if a woman has a hysterectomy, we generally don't say she's no longer a woman.
- Many people who can have children don't identify as being a woman.
- Having the capacity to bear children doesn't imply that this is your "greatest value." This is a normative statement, not a factual one. You can't prove a normative statement from factual statements. [1]
- We don't organize our society around biology. We weren't born with wings, but we fly. A woman's biology shouldn't limit her ability to pursue her own happiness. If she doesn't want to settle down in her 20s, chiding her for letting her biological clock run down is patronizing, moralizing, and unjustified.
People don't get upset because the truth is too hot to handle. They get upset because this is a bad faith line of argumentation used to justify bigotry - getting upset is a reasonable reaction to that.
[1] https://en.m.wikipedia.org/wiki/Is%E2%80%93ought_problem