These really are simple questions.
---A simple question, what gives you the right to something I create?
The Constitution gives that right.
Not until the copyright protection prescribed by law expires. You and I may have some agreement about shortening that length of time, but the idea that you or anyone else has an inherent "right" to something I've created is simply false. As proof I offer the following. I have in mind a creative work, let's say a poem, but I've not written it down. There are only three ways you can get it from me, you can buy it, I could tell it to you free of charge, or you could threaten to kill me if I don't give it to you (i.e. steal it by force). Which one of these is not protected by the Constitution?
---Another simple question, what incentive remains for me to create anything if you will only steal it and say you had a "right" to it from the beginning?
Money is rather a bad incentive. In terms of psychological incentives, wanting to create for creating sake is much higher. And hence, the art forms that would rarely ever sell, but are created nonetheless. However, by cutting off money also cuts off the 99% of the works that rely on selling to the lowest common denominator.
And no, the second question is not a simple one. We're talking about money vs. a persons want to create.
That's great, but it's hard to eat on pursuing higher incentives. I also think you view of money as an incentive is very cynical. What else can you offer an artist who has created something you really want? Wouldn't you be willing to offer even more money for something you like better? This line of thought does not remove or diminish an artist's desire to create something great. On the contrary, it rewards it!
And as a question to you: Why should we allow artists who hold copyrights able to sell them off? Shouldn't artists be afforded all the fruits of their labor?
It is the artist who holds the right to the work. If I correctly understand your question, I would say it is buy selling their work that an artist enjoys the fruits thereof. The person or people that buy the work enjoy it as well and everyone benefits. If the artist would prefer to give it away that is also their perogative. But ask yourself, if you remove money as an incentive what is left? Would you spend your life making things, useful things, beautiful things, only to have them taken from you by someone claiming "rights" to them? Someone unwilling or unable to create those things on their own?