CAPTCHAs are discriminating. They fail at what their name suggests they do occasionally. Which means they dehumanize humans. There are humans without eyesight, you know? And some of these have bad hearing. The web has decided that it is OK to classify these people are computers. And nobody cares because the solution is so convenient. Well, thats how society works.
They do have somewhat accessible alternative modes. Give them a try (these are even more dystopic — try having it read out some numbers for you to type).
