No one because I don't believe in automatically discounting anyone's opinion just because I dislike it.
Great things never came from comfort zones.
boooooooo Goose booooo
For all you know, people with large ignore lists regularly debate their ideological opponents in other mediums, and Atlas is just one place where they would like to avoid them.
Also, there are more than ideological reasons to put people on ignore. Some users are just incredibly annoying or are impossible to have a reasonable conversation with because they are too partisan / too crazy / whatever.