The problem with your statement is the fact that, until a certain point in gestation when the fetus is capable of living unsupported by its host, a fetus is simply a parasite living off of said host for a number of months until birth. I can't bring myself to grant the full rights of personhood to a being who literally draws all of its oxygen, water, and food (not to mention waste processing) from another living being without giving its host a say in whether or not she wishes to remain a victim of parasitism.
Now before anyone posts trying to 'remind' me that I was the same way, yes, I was also a parasite in my mothers body for a significant fraction of a year. She chose to allow me to remain there, causing all sorts of physiological issues, until I was done gestating. That was her choice and I don't want others to be denied theirs.