And, to add to this, if a coin can't cope with the amount of coins given away for free, then it's time to re-think your marketing strategies, not following the rest of the herd to get a bounty campaign going.
Very well said. Sadly, most of the ICOs have no marketing strategy at all. I think their only strategy is to raise money no matter what, and these campaigns appear to be a convenient way to achieve that cheaply. I have participated in a couple of ICOs and I have experienced first hand what you describe as bounty hunters dumping the coins immediately. There is a constant fear that the price is going to go down. If the project is legitimate, the price will go down for a short period of time, followed by a rise. But not all projects are legitimate. To prevent this, an ICO may choose to issue the bounty rewards sequentially, but I don't see happening often.