Abortion, quite simply, is murder. And, as such, it should be illegal and is highly immoral.1. Murder:
The four characteristics of life are present at fertilization: Growth, reproduction, metabolism, and response to stimuli. 
From the moment of fertilization, a living human being is growing. It has DNA distinct from its mother, and is not just a "clump of cells." 
With ultrasound technology, we see the baby moving around in the mother's womb.
Scientists have also documented a "flash of light that sparks when a sperm meets an egg" at conception.  2. Illegality of murder:
Our country has laws against manslaughter. Therefore abortion should be illegal.3. The Moral case for illegality:
Globally, 56 million abortions happen per year. 
To put this number into perspective, the most generous estimates of the holocaust pit the number of jewish deaths at 6 million throughout all 12 years. 
So, in one holocaust year, 500,000 jews died, but in one abortion year 56 million babies die.
To compare numbers, if we took abortion and stretched it to 12 years, 672 million babies died within an equal time span to the holocaust
Now, abortion is a very violent process. A baby is sucked out of a woman like a crumb is sucked off a table. 
And if a baby somehow manages to survive this process, it is often murdered on the spot.
Unconstitutionality of Abortion:
Abortion is unconstitutional due to the very first sentence of the Constitution:
"We the People
of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility
, provide for the common defence
, promote the general Welfare
, and secure the Blessings of Liberty to ourselves and our Posterity
, do ordain
and establish this Constitution for the United States of America." 
Until you can prove that abortion does not remove liberty from our posterity, then you must agree it is unconstitutional.
Our posterity has a right to life because they have a right to liberty.
The very definition of "posterity" according to Black's law Dictionary is as follows:"All the descendants of a person in a direct line to the remotest generation. Breckinridge v. Denny, 8 Bush (Ky.) 027."
This means that the Constitution protects ALL DESCENDANTS of a person's right to life. An abortion effectively takes away that right. Therefore, it is unconstitutional.
But, just to cement this further, the U.S. Code does, indeed define "child":"A person’s 'children' are that person’s immediate offspring, whether legitimate or not, and any children legally adopted by that person."
Being as "immediate offspring" is present in the womb at the moment of conception, then, clearly, their right to life is constitutionally protected and the Government has a duty to protect it since it must "provide for the common defense" of its citizens and posterity.
Therefore, constitutionally, abortion must be abolished. It deprives a posterity of the right to life, and the government must oppose such things to fulfill its constitutional duty.