1. Hoarding of food items is DIFFERENT from hoarding of other things. Food items are next to oxygen in terms of urgency in need, hoarding them is like stopping someones oxygen then asking for money to release it. Hoarding of non-urgent goods like real estate or gold has no such (blackmailing) effect because buyers have the power to not-buy until sellers cannot afford to hold the land anymore.
2. For every person who buys land today in order to sell 10 years later at profit there is someone else who had purchased 10 years before and wants to sell today in order to meet his financial needs. So hoarding by one "hoarder" gets cancelled out due to selling by another previous "hoarder".
3. Making a profit on your land holding seems perfectly fine because it involves risk taking and tying up your money for some future buyer who can afford to buy in a fully developed area instead of buying and waiting for a long time. So basically you are giving a service.
4. If too many people start hoarding all of a sudden then the price in market WILL go up BUT this will also create incentive for builders to develop more land which will bring the price down again after a while. Market will always go back to an equilibrium between demand and supply no matter what people do.
5. If you are "hoarding" only to make a profit and for no other reason then probably there is Zakat due on the value of land (please confirm) which a lot of people probably do not pay but that is a different topic. 
