> the government keeping a secret list of a certain subset of its citizens certainly leaves a bad taste in my mouth even if I can't perfectly express why
Some possible reasons:
* Because the government is of the people, for the people, and by the people, it may not discriminate against a subset of the people for any reason that isn't a direct result of due process procedures
* Because lists and tools like this have historically been really good at facilitating discrimination against the people on it, and that it doesn't take terribly much to imagine a politically motivated party loosening the criteria for inclusion on these lists such that people from a certain country are easy adds, furthering discrimination against them
* Because a government under the American constitution only has authority by the consent of the governed, and we clearly cannot consent to secret lists that we cannot see or verify our membership / non-membership in
* Because often, the government uses inclusion on these secret lists to justify restriction of rights or privileges to those on it, as we have done in the past to restrict gun rights based on one's membership on the no-fly list
* Because oft as not, the government is really bad at keeping these lists free of false positives, such that senators, children, dead people and others have been mistakenly added, and
* Because the government is loath to remove people's names from the list, even where the names can be proven to have been mistakenly added, causing weird scenarios in which Muslim people who were fraudulently placed on the list have to sue for the right to sue to be removed from it
* Because these lists have been, and can in the future be easily turned against one's political opponents with a handful of keystrokes