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"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:

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

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

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