Horse meat is legal outside the USA and is regularly consumed. In places like Europe it is a delicacy and is found in some ground beef products. There are a number of reasons why you should not eat horse meat.
There are medications given to horses that can be harmful to humans. The medications given to horses are not meant for horses that will later become food.
The way people kill the horses are often very inhumane. They shoot the horse in its head a number of times until it stops moving. They then cut its throat, drain its blood, and sent it to a meat company.
People don't always keep records of their horses. For instance, a rescue horse may not have all their records in the possession of the new owner. Any horse can be brought to a slaughter house and have their meat sold.
There is no good, or safe, way to bring horse meat back to the USA. How would you like to have horse meat start showing up in you hamburgers and meat balls? Many people are against eating horses, and if animal cruelty is illegal, horse consumption should be to!
I have many sources which will give you more information. They are listed below.