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?
If you choose the right airdrops, then nothing bad will happen. Yes, many airdrops do not even pay, but you can get into really interesting projects for free. The main thing is not to show your private keys anywhere and not to send any Deposit.