But every bank has different rules for churning, and you have to learn them, not ignore them and then fume about how stupid they were, when it was you who didn't take the time to learn them.

There are degrees of churning. Some banks (including Barclays) are ok with "light" churning, some other banks (Citi) can also deny you in cases like "more than 6 inquiries in the past 6 months" (on whichever credit bureau they pulled), which can also backfire on "very heavy" churners.

So not all churning is the same!