Join Date: Sep 2006
Location: Princeton, NJ; Lviv Ukraine
Programs: UA 3.6MM, AF/KL Lifetime Plat, BA Gold, AA 1MM, IC Spire RA, Kimpton IC, Marriott Plat, et alia
Posts: 2,732
What's the big deal?
They will eventually require to see your passport when you check in! The passport number WILL be entered into your record. This is mandatory for virtually every international flight everywhere.
It is used to ensure you have the right documentation (visas, proof of onward travel, sufficient funds) if required. In most cases, the passport details are transmitted in advance to the arriving country for pre-matching (Advanced Passenger Information Systems).
If this information is in the record ahead of time, it will expedite your check in. This is a good thing. And if you can check in faster, so can the person behind you, and so on. Faster checkins. Shorter lines. Means you wait less. Means you can check in later than if you have long lines. Faster immigration checks.
Why would anyone see a problem with this?
You might as well say that you should not enter your NAME into the reservation because you'll give it again when you check in!