Yes, it might be, but paint isn't.

You move the machine to the left and the right and when you see you're exposing the concrete, you move on to the next section.

This method is commonly used to sand the polyurethane off of hardwood floors, and so as long as you don't try to sand the concrete down, it'll work on a porch.

In fact, one Canadian janitorial equipment manufacturer, Centaur, makes a floor machine called the "Woodpecker" specifically for sanding the polyurethane off hardwood floors. It is used along with a vaccuum cleaner to simultaneously vaccuum up the sanding dust created.

http://centaurmachines.com/wp/wp-con...oodpecker1.jpg

http://centaurmachines.com/wp/wp-con...oor_sander.png

And besides, at $5 to $15 max for a sanding screen, you can remove a lot of paint for $10.

You just have to be careful using it on concrete because high productivity pads are only about half the thickness of a regular floor machine pad. A person could always use two high productivity pads and a Big Mouth to hold them concentric.