Hello Piotr,
I think if the project isn't transparent with planned distribution of Token via airdrops upfront they are cheating the investors.
The worst example in this regard to me is TenX IMHO. From the start they promised returns on the token that they later could not deliver because of regulatory issues, credit card providers (TenX should provide a on/off ramp to/from crypto by own credit card with own wallet) that changed or moved out of the business relation ship with TenX and so on.
In 2018 they then came up with the following solution to provide the promised returns they will build another token that will be distributed to TenX holders but - and here's the big catch - only to non US citizens and all the others that want to receive this secondary token must got through KYC also. So no secondary coins for me since I'm US citizen.
Other projects that laid out a token distribution plan that includes Airdrops to ETH holders for instance (we all have seen this with a lot of projects where the only thing that qualified you for the airdrop was to be an ETH holder) seem to be alright in that matter.
On the fly without stating airdrop intentions is, and here you are completely right (!!!), definetely cheating the investors!
We could make a really big list here but most prominently in the recent past there was Tron with their BTT Token. Very questionable IMHO.
So all in all... I like free money but I like full transparency in projects more!
Still I'll participate in some airdrops nevertheless regardless of transparency issues, because it's like leaving money laying on the ground and being too lazy to pick it up if not.