The outcome was fair. That was a scandalous red card and a rule that exists to be sparingly used in situations like that was triggered. Hopefully it will keep being sparingly used but they should not hesitate to overturn unjust punishments that are clearly against the spirit of soccer.
Why are people so upset about it? Is Belgium afraid to face the full US squad? If Belgium wins, which is the most likely result, nobody will be able to say "the US could have won if it wasn't for that red card!"