The true airdrops must be free or at least make the payment optional (voluntarily), all you need to do is to complete some tasks, which should not be monetary. Though you have a point, the project matters, like the Testnet and others, but this Testnet of a thing was not like this in the OP, people knew what they were signing for and it was honourable when crypto was still crypto and not how everything was turning now.
Many would even participate in the Testnet and will not expect anything in return because they believe in a project, so it's just like technically sponsoring the project in their little way. But there are too many crooks flooding the internet in the name of airdrops now, especially Telegram and mostly now the TON blockchain. It's just annoying and even their tokens after listing are often worse shitcoins. The success of Notcoin has made them gain popularity but this will soon fade away just like their former ways of toying with people's emotions in the name of airdrops.
We can see it when there is a popular and profitable project. there will be thousands of scammers. we also saw some time ago how the airdrop on the Solana network was popular and many tokens were born and then disappeared.
It will not be much different from what is happening now on the TON blockchain. you are right, airdrops should be free. no fees to claim NFTs or make deposits to increase mining speed. we see a lot of such projects now. maybe not all of them are scams, but more of them end up scams.
Though one case would be a rent for the NFTS on the chain - if for signing a contract for such an NFT a bit of TON is needed - it's okay and it's no scam, as far as I know. It's a rent to get in on the chain for a year or for the time it's needed.
That's just what popped up in my head.