Every single deck you ever play against will immediately try and take out your eldrazi, and without spellskite your chances will drop tremendously
Cards that retarget things might not always be what you need at the moment, but when they are, they tend to create epic moments
By turn five, you can expect to be cheating out huge mana-value creatures, like Demon of Death's Gate or Pestilence Demon
Non-red decks have plenty of answers too
Its also really easy to break, as all you need is two creatures that can flicker each other, which not only produces infinite +1/+1 counters on your creatures, but also scales firebending up to make infinite mana when Zuko attacks
If you want to know which is better, check out my rankings of the swords