At the outset I will declare my commitment to the right of women to terminate pregnancies prior to the time a human being has developed in their bodies (roughly the 25th week*). But then I am also someone who holds that every adult individual has a full, unalienable right to his or her life. (Who else would?)
But one of the contemporary Left's favorite doctrines, communitarianism, doesn't agree. By their standards we belong to the community. Check out what Charles Taylor says about this in his book, Sources of the Self, or, even better, read the famous American Leftist, Cora Weiss, who was a prominent American anti-war advocate during the Vietnam era and claimed that refugees who have fled Vietnam were traitors because, she argued, "Every country is entitled to its people [who are] the basic resource that belongs to the country." (Washington Post, May 29, 1978)
Weiss was by no means alone in her views. The East Germans argued they had full moral authority to shoot those trying to scale the Berlin Wall because such people were stealing themselves from East Germany, from the country. Then there is the famous Marxist doctrine of the labor theory of property according to which the source of all value is human labor which, however, is public property since it is the major means of production that under socialism is collectively owned.
Softer Leftists, such as communitarian Michael Sandel, also contend that our lives are from birth beholden to the community and we do not have the full right to it. This reiterates the views of the father of sociology, Auguste Comte, who wrote this about the topic:
"Everything we have belongs then to Humanity...[Comte's] Positivism never admits anything but duties, of all to all. For its social point of view cannot tolerate the notion of right, constantly based on individualism. We are born loaded with obligations of every kind, to our predecessors, to our successors, to our contemporaries. Later they only grow or accumulate before we can return any service. On what human foundation then could rest the idea of right, which in reason should imply some previous efficiency? Whatever may be our efforts, the longest life well employed will never enable us to pay back but an imperceptible part of what we have received. And yet it would only be after a complete return that we should be justly authorized to require reciprocity for the new services. All human rights then are as absurd as they are immoral. This ["to live for others"], the definitive formula of human morality, gives a direct sanction exclusively to our instincts of benevolence, the common source of happiness and duty. [Man must serve] Humanity, whose we are entirely." Auguste Comte, The Catechism of Positive Religion (Clifton, NJ: Augustus M. Kelley Publ., 1973), pp. 212-30.
Okay, so what of this? Well, it is entirely inconsistent with the stance on abortion of most of those on the political Left in America. They are pro-choice. But pro-choice means having the right to do with one's life as one wants, provided it is peaceful. And so long as abortion isn't homicide, it is peaceful and every woman has a right to get one if she so chooses.
However, if one's life belongs to humanity or society or the community or the state, this pro-choice position on abortion − and on innumerable other matters − makes no sense. In general, the Left rejects the idea that choice is a vital element of human life. Instead, what matters is obligation (or duty) to others (or to humanity or society)!
This idea is the ancient one, whereby everyone belongs to the country, the king, the tzar and so certainly it is utterly selfish to insist that one's life is one's own and that from this certain rights follow, even the right to terminate a pregnancy at an early stage. The left simply has no basis for insisting on this. (Not that the Right is much better. But I leave that for another time.)
*This isn't geometry but biology so the exactitude is appropriately fuzzy!