Abraham Lincoln said, "If slavery is not wrong, nothing is wrong," and I agree with his sentiment. I should note, however, that I disagree with many of Lincoln's political assertions. Yet the above quote is not political. It is a moral statement recognizing that anyone appealing to justice and human rights must be against slavery.
In modern times, we simply know that slavery is wrong. Few, however, can express why.
In a nutshell: The institution of slavery was an established system of legally sanctioned inequality. When you take another man's liberty, you take his life. When you make a man your property, his property is made yours. Therefore, slavery violates the sacred principles that established this republic: "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty, and the pursuit of happiness."
Those who defended slavery from its critics appealed not to what slavery did to enslaved men and women, but to the "benefits" of slavery--race control, and the economic health of slave owners. If slavery were abolished, then blacks could roam the country freely! If slavery were abolished, then much of the South's economic capital would simply vanish into thin air!
These concerns were real. There is no doubting that slavery both kept blacks under control and propped up the South's economy. White men and women throughout the country feared the social equality that might follow black mobility, and economic interests in the South (e.g. planters) and the North (e.g. textile mills) relied upon slave labor. Ending slavery would set blacks free and threaten the cotton supply. Of this there is no disputing.
Nonetheless, slavery was wrong, and there's no appealing to the inconvenience of abolition. Abolition hurt many, but slavery hurt more and deeper.
The same is true with abortion. If abortion is not wrong, then nothing is wrong. Abortion stops a heartbeat. It kills. There is no denying it. Saying that a fetus is not a person is as feeble an argument as saying that blacks are not persons.
The abolition of abortion will be inconvenient to many. It will put some women in uncomfortable positions. It will be costly to some women, families, and the state (which will certainly be called upon to care for unwanted babies).
But it doesn't matter.
Abolishing slavery ruined the planter class, but we are better as a people for it. No man has the right to build his wealth in such a way. Abolishing abortion will also have its costs, but they are worth it. No one has the right to kill another person simply because that person is an inconvenience.