In the first paragraph, the writer mischaracterizes the mysteries of pregnancy. The woman in this example knows that she has slept with more than one man, so she knows that paternity may be disputed. Her partner probably does not have access to that information. Additionally, she will have a better idea who the father is because she is aware of the timing.
If we are going to make men responsible for pregnancy support as well as child support, perhaps we should give the men the same choice that women have in becoming parents. If a man does not wish to be a parent to the unborn child, then allow him to extinguish his parental rights and be off the hook for further contributions of time and money. I think only an a*hole would do that, but then again only an a*hole would make someone a parent against his or her will. A man who chooses to be a parent will have to contribute his resources, and then will derive certain rights by virtue of his election and contributions like equal custody and visitation rights.