You’re saying every woman who gives birth should automatically be treated like a potential liar. Every kid starts life under a cloud of suspicion.
This is one way to look at it but not the only. I imagine people are sometimes incorrect about parentage without any intentional deception or malice. There are poly and swinger folk who are also drinkers out there not remembering some exciting weekends. You could go your whole life making medical, dietary or spiritual decisions based on a false family medical history.
There are camera and radio detecting devices available.