Hoarding in itself may not hurt and it contributes to the price but when a dump is made, it would make an impact especially a great number of coins were dumped. This is how others manipulate the price; it gets lower once a dump is made. Since bitcoin only has a limited supply and its supply does not change, hoarding or dumping and actions like these would make some effects and changes in the price. There are a lot who hoard and it is but normal for people to do so because they intend to have plenty bitcoins for investment.
What you are talking about doesn't only concern Bitcoin's market, but basically every market in the world since the basic principle of a market is based on supply and demand.
In the same way, every market gets manipulated by market movers. Bitcoin's market however lacks serious liquidity, which is why even today, a fair number of coins can get the market to plummet with like 10% effortlessly.
One thing is sure, people here love seeing the price go up, and for that to happen coins need to be taken off the market, but for whatever reason people still think it's against Bitcoin, or at least its currency aspect.