I'm going to chime in and agree with the guys above. If all you're going to pull is one of those little Harbor Freight special trailers (you know, the little 4x6 ones that fold in half?), then sure, go ahead and pull from the bumper on a newer truck.
But if you're going to pull anything that's got some weight to it, spend the money and get a real hitch receiver and draw bar, for a lot of reasons. Oh and get at least a 4-way plug installed so you've got lights on the trailer, even if it doesn't come with brakes and you don't legally need them. A 7-way round plug and a brake controller are a good idea.
First, that receiver is going to be able to take more weight than your bumper. You don't want the weak point in your system to be your hitch.
Second, you can pull the ball out and store it, while still being able to use the step in your step bumper. I leave my ball in place and use it as an additional step, because my big feet don't really fit in the step of the bumper very well.
Third, that receiver is going to have nice, sturdy points to hook your safety chains.
These just scratch the surface of why a receiver is a good idea instead of pulling from the bumper.
These aren't the old days when trucks had bumpers that could take a beating. Truck bumpers today are thin and meant to crumple to absorb kinetic energy.