That was the standard of his day. The Huns had been opressed and enroached on by various tribes and kingdoms, including the Roman Empire, and they acted within the expected mode of behaviour of the day, and were infamous only for being so good at it. That doesn't mean that Atilla's actions were good, but it does mean he wasn't quite so evil as someone doing those things today, and certainly not as evil as many warlords of the 20th century, like Stalin, Hitler, or Mao.