I don't think airdrops are ponzi-schemes but they are premined scams.
People are trusting the devs that they'll distribute the coins fairly while there are no guarantees at all for that. And cryptos should be absolutely trustless so airdrops (and ICOs) are taking a huge step backwards.
Also, people can buy bitcointalk accounts (legal but discouraged) and participate in airdrops multiple times.
So the "devs" might have 50 sockpuppet accounts they ask coins to. It's basically the next iteration of the "x% premined" scam as it is not that transparent.
Apparently that is what NEM did. They try to deny it, but when it is pointed out that they refused to even use Facebook verified accounts, they just claim that verifications were done but dont provide any independently verifiable objective proof.
And Byteball airdropped to exchanges who held so much BTC, so guess for yourself if any kickbacks were involved.
EOS runs a year long ICO no rights token sale ostensibly so they can buy said tokens from themselves.
Much better they did not try to hide the centralization of the money supply and the control over the ledger, e.g. Byteballs 21 witnesses are thus elected and controlled by these whales (and thus receive all the transaction fee income).
there was an airdrop for decred, but decred is really a good coin
Seems I had a debate with them some months ago on BCT and it was analysed how their system is really designed for the whales to control and milk.
Yall are so gullible.
I want to reiterate that even if the money supply of [OUR TOKEN] is centralized, the power over the consensus algorithm remains decentralized and controlled by the transacting majority (automatically & objectively, not by voting). This is what makes our decentralized ledger technology so superior as well as the performance.