One, the whole cell analogy is dumb on many levels. Going by the same logic, I can punch or hurt anyone I want and say I punched a lump of cells or something. Obviously, a human child in a mother's womb isn't the same as any other life form in the form of a cell. We, as humans, value human life more than anything else.
Two, my body my choice argument doesn't always hold true either. I can't hurt or kill myself just because it's my body. You don't get to beat children just because you gave birth to them. So there are limits to this. I do believe that women should have the final say in any matter involving pregnancy. But that doesn't mean they should be able to do whatever they want without accountability.
Three, unwanted children: this is a broad area but this doesn't work in a lot of cases either. If you gave birth to a child and started resenting it after a month or a year, you don't get to kill them and call it a day. Abortion should be the same. Don't kill babies just to skip responsibility, period.