Bounty hunters are alwasy blame for selling their tokens so quickly without waiting for the project develpment as outline in the roadmap. I don't think bounty hunters are to blame because a lot of bounty hunters hold their coins for years.
One thing to consider is volumes. Often they are very thin with newly listed coins coming out of an ICO. If a coin raises $10 million at $1 a coin, and then starts trading and drops to $0.1 per coin, then this isn't necessarily dumping - if volumes are only $10,000 per day, then what it means is most people are holding, and a tiny minority are dropping the price, and it also means that even though you can pick up the coins for cheap, you can't pick up many without exhausting the order book.