[arethuza]

"It excludes the letters I, L, and O to avoid confusion with digits. It also excludes the letter U to reduce the likelihood of accidental obscenity."

Excluding ILO doesn't seem a bad idea - but leaving out U for that particular reasons seems downright weird:

https://en.wikipedia.org/wiki/Base32#Crockford's_Base32

[inopinatus]

It doesn’t exclude them. Ignore the Wikipedia text, and look at the decoding table instead.

[arethuza]

True - they should be generated during encoding but are allowed during decoding:

https://web.archive.org/web/20021223012947/http://www.crockf...

[munawwar]

base58 avoids 0 as it looks similar to capital O in some fonts. Seems more reasonable than U.