Look back at the other posts. Someone specifically claimed unborn children are not human. The claim is made EVERY time this topic is discussed, and not always by the same poster. Therefore it is a widely held opinion that is easily proven false by science.
As such, it is not strawman as long as people make the false claim that unborn human children are not human. They make the claim, science refutes it.
As for the difference between a legal and biological, it is again not strawman. First, every dictionary on the English language defines a person as a living human. Second, what is the justification for excluding ANY living human from the legal definition of person? What is the justification for stating, essentially, that the scientific definition of living human is not good enough to be the legal standard? What is the justification for taking the stance that legal OPINION should be the standard for determining who has basic human rights, and who does not?
The problem with accepting the idea that opinion can/should be used to provide the legal definition of person is opinion varies, both between people and over time. There was a time when the legal opinion was that my people were not granted human rights. There was a time when the legal opinion was that blacks were not fully human, and could therefore be owned like cattle. Even today there are cultures that use legal definitions of humanity to exclude targeted classes of humans for discrimination, and sometimes elimination.
How is saying "the unborn may be biologically living humans, but aren't worthy of human rights" any different from the time when prevailing opinion stated "blacks may be biologically human, but they aren't worthy of human rights"? What is the functional difference between excluding the unborn from protection under the law, and excluding any other class of living human being from protection under the law?