I don’t see how it is any more problematic that maize (called “corn”, or technically “Indian corn”, in North America)? They are both “New World” grains used to make bread.
One should note that the machmir opinion in the gemara is that anything you make bread from should be treated as hametz (in that case, they were talking about rice), but the Ashkenazi opinion is more liberal and treat them as kitniyos. It does seem that someone who holds by eating rice and corn, should have no issues with quinoa, though there might be issues with making hallah, pita or pizza our of them.
Personally, I don’t use any of them, at least for food for humans.