In some states, it is legal to kill a person if they are in your home without permission. In other states, it is illegal.
In most states, it is illegal to help a person kill themselves. In at least one, it is legal.
Criminal law is primarily a state issue, and different states have different rules about manslaughter and murder, just as they have different rules about many things.
We also have the 14th amendment which was supposed to stop the south from mistreating blacks who were now free. It provides all people with the same rights.
But states are allowed to consider circumstance -- hence the "kill inside door=LEGAL, kill in front yard=ILLEGAL" that some states have. A state might decide that a baby inside a womb is in a special circumstance that they make it legal for the mother to terminate the pregnancy.
I wouldn't agree with that, but I understand the logic of it.
I said “murder,” not “kill.”