Unicode's mission is to make every document "roundtrip-able". Even if a character is only used once, it should be possible to save a plaintext version of the containing document without losing any information. Roughly, I should be able to put a transcription of that one translation from the 1400s on Wikisource without using images.
You may disagree with me, and that's fine, but it doesn't change Unicode's mission. Besides, there's room for 1,112,064 codepoints[a], and only 149,146 are in use. It's predicted we'll never use it up, so what harm is there in one codepoint no one will ever need?
[a]: U+10'FFFF max; it used to be U+FFFF'FFFF, but UTF-16 and surrogates ruined that
You may disagree with me, and that's fine, but it doesn't change Unicode's mission. Besides, there's room for 1,112,064 codepoints[a], and only 149,146 are in use. It's predicted we'll never use it up, so what harm is there in one codepoint no one will ever need?
[a]: U+10'FFFF max; it used to be U+FFFF'FFFF, but UTF-16 and surrogates ruined that