You can actually have 9 queens. There is no such rule.
Promote to a second Queen

The laws of chess does not prohibit polygamy. Albeit many strong players know that multiple queens tend to redundant on an crowded board.

I do not agree that it is unfair at all. But (I've heard) many players learned chess believing you can only promote one queen, simply because most chess sets have only one queen! Since they learned that way, it can often be frustrating when you discover that those aren't the rules. Like how you probably felt the first time someone used en passant on you.

Actually, the "free promotion of the pawn" is one of the latest adjustments to the chess rules, as we know it today. Back in medieval times they've played it like you can only promote a pawn to a piece already captured.
But then they thought it's a silly restriction standing against a good and fluent game. If you're able to get your own pawn into the back rank of your opponent, why restrict this achievement.
The rule is neither silly nor unfair because your opponent has the chance to do the same all over the game.
What do you think? A nonsense rule or not?