Не "что бы", а "чтобы"

Как-то так должно быть: паспорт на то и паспорт, чтобы = для того паспорт и существует, чтобы = that's what the passport is for, to put the marks into it (поправьте, если что не так во второй части).

Ули, отличный вариант. А можно так, как у меня?

Спасибо, Дмитрий. Your version is possible if somebody has several documents besides the passport and offers one of them to get stamped. You could say: "No, that's what the PASSPORT'S for - getting stamped." My version is used, for example, if someone doesn't want the stamp because he wants to keep his passport clean: "That's what passports are FOR - getting stamped." (capital letters show stressed words)

Thanks, Uly.
Your later version (if someone doesn't want the stamp because he wants to keep his passport clean) and its translation - is exactly what I meant.

Ah, got it. Thanks for the clarification.

DImanne, that's what I thought - I'm glad I picked the right one :)

Anytime, Dmitry. Remember, when we refer to things in general or as a class, we often use the plural.