Intellectual property became established and recognized because it incentizes invention and creation which drives the economy. However companies have at times invented or discovered something, patented it and then decided not to use it and also not to contract out to allow others to use it. This defeats the entire purpose of intellectual property and the United States should use its eminent domain powers to create a "use it or lose it" rule to make sure intellectual property can not be inverted away from its true purpose and used to advance personal profits at the expense of economic innovation and progress.
Will a person be required to sell a certain number of their invention? Where is that number determined?
Does it differ from invention to invention?
What if a person is still engineering their invention? Do they have a time limit they must be done by? If so, why? Who is to say the invention simply isn't complicated and taking a long time to perfect? Doesn't the holder of the patent have a right to decide when and how he will use his invention? If not, it is hardly his property in any sense. This does not give the holder of the intellectual property sufficient control of the use of his property.