Some individuals or companies have abused the TrackBack feature to insert spam links on some blogs (see sping). This is similar to comment spam but avoids some of the safeguards designed to stop the latter practice. As a result, TrackBack spam filters similar to those implemented against comment spam now exist in many weblog publishing systems. Many blogs have stopped using trackbacks because dealing with spam became too burdensome.

Pretty much any standard that automatically displays content on a page has to have anti spam provisions from it’s inception or it’s doomed. Not all people are evil, not even most people, but the ones that are asshats have a disproportionate amount of effect on the activities of others.