Thinking further about abortion-related issues tonight ...
IMHO, the difference between progressive and libertarian thought comes down to this:
Libertarians assume that if government/society (and, occasionally, religion) simply gets out of the way, everyone will be free to make whatever choices in life make them happiest.
Progressives know that without a public framework in place to ensure that everyone, no matter where they start in life, has access to every choice available, there is no such thing as true freedom of choice.
We are not born omniscient. The advantages of information, self-sufficiency and social autonomy that many take for granted are NOT universally available to everyone the instant they're born. We are born blank slates, and we learn only that which is made available to us in our immediate environments: family, community, etc. Likewise, we are not all born with access to sufficient money, health care, education and other means that everyone needs to navigate the world.
A fatal flaw I see in a lot of libertarian-leaning folks (and some progressives who don't get this) is that they look at the world from an incredibly entitled position. They're middle class or higher. They're male. They're able-bodied. They're straight. They're white. Etc. They simply don't understand that all of those things have given them huge advantages over others from the moment they're born, and so they assume that if anyone is in a dire situation as an adult, clearly it's because they chose to be that way.
Even something as deceptively simple as getting enough vitamins as a child is something that can have huge repercussions later in life, and it's not something that every child has. Public schools and libraries? Sure, most Americans have access to them. But their quality varies wildly along class lines. Time and bandwidth to study hard? Easy for most middle class kids. Not so easy for a kid who has to work part-time to support the family, or has to take a lot of time to care for siblings or ailing relatives. And once those pillars of childhood success crumble, there's just no way to build anything strong on top of them and have a successful adult life without either a hell of a lot of help or sheer damned luck.
People with privilege feel free to make choices because they've always had a full range of them--and information to help them make a choice--readily available. They don't understand that people without privilege often make "choices" that really aren't choices at all. An educated, middle class woman, for instance, may choose sex work because she enjoys it, and it pays her more than a boring office job. A working class or poor woman may choose it because she has no other way to pay the rent or feed a child, or because she was trained as a child to believe that her sexuality was her greatest value. So can we assume that every sex worker isn't being exploited just because there are some middle class women doing the work by choice?
I think a lot of people with privilege don't want to acknowledge this reality because it's easier to assume that everyone has autonomy. It absolves us of any responsibilty to make our own choices with the well-being of others in mind. If we can pretend that that "welfare mom" down the street just chose to be an indiscriminate slut, instead of acknowledging that the circumstances she grew up in forced her to make the choices she made, we don't have to care about her, and we don't have to do the incredibly hard work necessary to ensure that she truly does have choices.
This does NOT assume that people without privilege are stupid or lack the ability to make decisions. It doesn't mean they're weak, or to be pitied, or are incapable of gaining autonomy. It only acknowledges the reality that none of us is an island, and that control over our lives and the range of choices we have availble for them is not something everyone can determine for themselves. Unless we know for absolutely certain that a given person is fully aware of and has access to every choice possible, we cannot, in any way, insist that the choices they make are truly their own.
It should be no surprise that most libertarians are either people who already have a ton of privilege (straight, rich, white guys, mostly) or people who are so far down the ladder of power that they are incredibly sensitive to any notion of control over their lives, and so are suceptible to the lies told by the other half of that body about how it's only government excess getting in their way. It's incredibly painful to have to admit that you don't actually have a lot of power in our current socioeconomic/political system. The vultures quickly descend on anyone who shows such signs of weakness. So it's far easier/safer to just wave one's fist at this faceless "government" entity, and say that The Man is the only thing keeping you down. Contemplating the reality that no, it's actually Your Fellow Man doing the oppression, is just way too damned depressing. Not surprising people don't want to do it.
And it's for the sake of those lost souls--those people who are so desperate that they've been led down the path of their own destruction by those cynical, objectivist pied pipers--that the rest of us have to stop accepting those lies as just legitimate political philosophy differences, and start working toward a world in which everyone truly is born equal, and what they come to in life is a matter of their own will.
As the bumper sticker says: no one is truly free while others are oppressed. And if we continue to allow this oppression under the idea that overreaching authority is the only thing standing in the way of everyone being free, happy little clams, we are shirking our responsibilities as human beings in a civilized society.