What part of KIDNAPPING wasn't clear? Showing up in a "Masternodes" event is way worse than giving your ID card or Social Number. It may be safe in your country, but it isn't everywhere in the world. You can be followed or arrested after the event, and you're done!
What IF the number of atendees and number of papers doesn't match? An electoral process with a physical "ballot box" is a centralized process. Who's going to be in charge? Why should we trust them?
Let me asnwer your above questions.
Its not a masternodes event. It is an empty_dash_wallet holders event. There is no kidnapping risk! You are among ordinary people who are not masternodes, and who may attend the same meeting in order to get their universal dividend. There is not ID card or Social Number required. And it is totaly safe, as long as you do not advertise eponymously (in your everyday life or in the internet) that you own a masternode . But even in the case you did the mistake and everybody knows that you are a masternode owner, the cryptoparty procedure allows you to appear masked, so you are safe that way (as long as, of course, you are not the only one masked and there are many other masked people that attend the same cryptoparty).
You will not attend the cryptoparty with your private keys! You participate by having several empty_wallets (their public keys) printed in QRcode. During the cryptoparty (which takes place in a closed door room where nobody is allowed to leave until the procedure ends) everyone puts one QRcode wallet in an envelope and then the envelope into a physical ballot box. Then all the wallets are extracted from the ballot box, they are counted, scanned, added in a digital list, and their number is expected of course to be found equal to the number of the attendees. If someone objects that the list of wallets is not equal to the number of attendees, or if he claims that his wallet is not into the list, then the voting is repeated, and until nobody objects (due to the possibility of voting repetition, everyone should have more than one printed QRcode wallets pre-created, so that he can re-vote in case an objection occurs). Finally, when there is no objection, everyone receives the final list of the valid wallets, the door opens and the cryptoparty finishes. All the wallets that are contained in the final valid list, can be considered now as a proof of individuality, that can be used online in the internet. And as long as every single attendee is allowed to object, this is considered as a decentralized (and unanimous) process, isn't it?
For even more decentralization, many similar cryptoparties may be organized in several towns, as long as those cryptoparties are absolutely concurrent, and a web of trust among cryptoparties is established so that all the wallet lists of all the cryptoparties are recognized as proof of individuality. A web of trust among cryptoparties means that all the attendees of a specific cryptoparty sign whatever else cryptoparty they trust it is legitimate. This multi-signature may occur immediately after the creation of the final valid list of wallets, and just before the door opens.
Having your proof of individuality (I remind that you put it into the ballot box, so it is anonymized), you can now claim anonymously in the internet your masternodes, by signing the dash addresses of your masternodes with the private key of your empty_dash_address which you put in the ballot box, during the cryptoparty.