I would say that we all have a moral obligation to support everyone who needs support, but that we are all constantly failing at this. However, one should not be unduly concerned about this, as this is not a problem that one person or even an entire country, can solve alone.
So why should anyone be unduly concerned about abortion?
Even if we accept your premise that a single cell can be a person, why should that person evoke
more moral outrage than the millions of people who die of preventable causes each year (including several million actual children).
The issue here is not just how much of your personal wealth you have sacrificed for others, as you point out that is indeed a fairly small contribution in the grand scheme of things (although not as small as not having an abortion, even if we accept that that is a contribution at all). The bigger issue is what, ethically and politically, you have done to advocate for those millions of people, again including children, who die preventable deaths due to living in an unfair economic system. Do you advocate for them with the same zeal with which you advocate for the protection of single celled zygotes, or are the zygotes somehow
more important for some reason?
Why can't it be both? Frankly, responsibility needs to be enforced. A lack of responsibility causes so many problems. Fathers might not feel responsible for their children or their baby mommas, who, in turn, might not feel responsible for their baby daddies or children. This leads to broken families, broken homes, and broken people.
Do you seriously believe that a family consisting of people who are forced to be together out of desperation and coercion is not a broken family? Do you believe that is a healthy environment in which to raise a child who, from the day of their birth, is unwanted and unloved by the only people you feel are responsible for them? Do you believe that environment produces healthy people who are not, in a very real sense, broken.
This is why it cannot be both. You cannot care about the wellbeing of a child, and also be determined to use that child as a weapon against its parents, or as a way of forcing them to live the miserable, shitty life you believe they deserve for falling short of your moral standards. Using a child in that way is inherently harmful to the child and, ironically, is deeply inconsistent with the idea that they possess an individual personhood worth a damn.
If you have sex, you need to deal with the consequences. That's responsibility. Aren't ready for the consequences? Then don't have sex.
Are you willing to apply this to the unintended consequences of actions generally, or only to the consequences of actions which you personally disapprove of?