On what basis should airdrop be stopped? Basically, Airdrop is a means of promotion and aims to develop the ICO project community.
Even if it is stopped, their community will be quiet and signify that there is no support for their project and investors will not interested to follow and participate in their ICO's project.
In fact, the tokens found from Airdrop are very low. But if the community supports it, maybe a few months ahead the price of the token is much higher (except scams project).