If you're approaching this from an "ethics of sharing" stance, then what what you're actually restricting is somebody else's use of their own code. Your code never disappears/changes/gets relicensed, it's their code that you're staking a claim to.
Now, if you're approaching this from a stance of withholding certain valuable rights to your code, such as the ability to be the only person that licenses closed source usage, then the argument is a bit more logical.
> They are free to open up their code to me if they want to use mine.
I do. Under the MIT license.