The title of this thread is bit provocative, but the fact is that most people have a bad experience with airdrops. According to several airdrop hunters I spoke to, the majority ICOs don't pay out at all.
What's your experience with airdrops? Did you get scammed most of the times?
Airdrops cannot be a scam by definition, since nobody pays anything to get the free token. However, it is true that most of airdrops are a total loss of time because there is basically no project behind, just the intention of the devs to make some free money for themselves.