Airdrops don't necessarily equal scam. Airdrops can be a suitable method for distribution of a new coin as oppose to the ICO route. Additionally, look at the coin and it's development. Is there a viable product? Is there movement? Is there developer communication? This are the questions that determine if something is a scam, more so then airdrops/coin allocation.
Additionally, how is an propositional airdrop in relation to the amount of coins owned be a scam. Early investor and large investors take significant risk to help up a new coin, propositional distribution is the fairest model for airdrops. If you want more, buy more.
Additionally, I see a number of post calling it a Ponzi scheme, if that is the case aren't all coins a ponzi scheme. Early adapters earn the greatest returns.
Consider the facts before labeling anything a scam, just because it offends your sense of fairness, as oppose to the reality of the situation.