You're 100% entitled to do what you want with your own property but please consider the view that domain names are important and finite resources and should be put to good use :)
Or any other commodity.
If instead the initial registration was taken as the sale of a commodity, the original way they were distributed didn't make a lot of sense. It would've made more sense to auction them off at fair market value, rather than registering new domains first-come/first-serve for a nominal fee.
I suppose that ship has long since sailed, though a few ccTLDs still retain that position, at least officially. DK Hostmaster's policy statement says that Domain names cannot be purchased, but borrowed. In other words, by registering a .dk domain name, you have acquired the right to use it. However they've given up trying to enforce that, and allow this "right to use" to be fully transferable, making it quasi-property. They still maintain a vestigial waitlist by which you can register to be next in line to receive a domain when the original owner relinquishes it, but this is in practice no longer used for anything that's in demand.