Kudos to them for using the subjunctive tense, though

Not only is it demeaning to liken women to cardboard boxes, but the analogy is completely daft, too.

SCENE: a box factory

NARRATOR: If you thought there was a small chance that a baby was hidden in a box, wouldn't you treat the box as if it held a baby, just in case?

SCENE: an ultrasound image

NARRATOR: So even if you think there's just a small chance that an unborn child is a baby, shouldn't you treat it as if it were, just in case? Something to think about.

The first example is that of a closed box with unknown contents, but you have some (inexplicable) reason to believe that the contents may contain a baby. In this scenario, sure, you might want to err on the side of caution just on the off-chance that someone decided to ship a baby via UPS. Or you might actually look inside the box so that you know what the contents are if you have reason to believe there's a baby in there.

The second case has absolutely no relation with that scenario; instead it relies on the bizarre notion that a fetus has "a small chance" of being a baby. But of course a fetus is a fetus, and a baby is a baby--the desperate need to conflate the two is always bizarre. Further, we might point out that women aren't black boxes. The stages of pregnancy and fetal development are well-known. To compare pregnancy with a closed box whose contents are unknown is just a testament to the determined ignorance of the anti-choice side.