When you see them next a human, how terrifying they would have been becomes quite apparent.
Below from the Wikipedia article on terror birds:
There were some suggestions that phorusracids, like the majority of Pleistocene megafauna, were killed off by human activity such as hunting or habitat change. This idea is no longer considered valid, as improved dating on Titanis specimens show that the last phorusracids went extinct over one million years before humans arrived. However, fossil finds in South America dating to the late Pleistocene indicate that Psilopterus, a relatively small form, may have been present until 96,040 ± 6300 years ago. If true, this extends the existence of this group of avian predators considerably.