It's more or less a publicity stunt for Planned Parenthood. They're getting tons of attention from this.
And I wouldn't say that this shirt is in particular poor taste after seeing this one:
http://www.tshirthell.com/shirts/tshirt.php?sku=a08
But then again, poor taste varies -- I can see a lot more stupid high school boys getting this shirt because they think it's funny than women who have actually had abortions. But if someone who's had an abortion wants to wear a shirt like this, I have no issue with it -- as long as they're prepared to deal with all the isht it's going to stir up, of course.