The 'unstability' of airdropping SBD is that it sets a precedent, making the future outlook for the system completely unstable. If loads of SBD just fell out of the sky today, who says that won't happen tomorrow?
Also, the value of any crypto-currency at the moment comes from supply and demand on the crypto markets. Therefore being an attractive investment opportunity benefits its users immensely (it simply makes the rewards for content curation and creation higher).
Revolutionary and principal about Steem is the fact that rewards in crypto-tokens are built into content creation and curation. You can imagine that the value of those rewards (i.e. the value of the tokens) is vital and a driving factor for adoption as well.