I'm not sure why people are so outraged at this. The US has every right to allow certain people into their country or not.
For instance, Canada just instituted the ETA program (electronic travel authorization). This forces all non-US and non-Canadian citizens to have to apply beforehand and give a lot of personal information to the government. My in-laws flying in from the US, being US green card holders but not citizens were denied boarding their flight because of this ETA that they had to fill out. It's an inconvenience but something they took in stride. our beef was that nobody was informed of this. (they traveled here two years ago with no problems by air.)