Are non-primary auto increment columns bad practice?

[olliescase]

I opened a pull request (#47704) that was rejected that added the ability to specify an auto-increment as a non-primary key for the databases that support it (MySQL, PostgreSQL, MSSQL).

I don't want to strong-arm this through - I suspect a lot of people will agree with Taylor. But I wanted to hear people's opinions on whether or not this constitutes bad practice.