A friendly advice though, do your own research before you will apply for them. Its free yes, but better do what is necessary to protect yourself.
what is the danger?
Is it bad to fill in a form with my user id and email and eth address?
what is the downside? let me know if i'm missing anything.
Thanks.
Some airdrops require wallet download, this can contain trojans
some you need to fill in too many details, you are setting yourself up to get hacked

i dont think your ETH can be stolen by just posting your public address, but if you post it with your name and email someone might be able to hack your email, which could contain info of your crypto.
Always be carefull!