Well actually in France both tying and denial of selling are illegals. ...
... But even without this, and after all I can very well understand that we should not force anyone to sell something if he doesn't want to. ...
... Even if I can't buy a Rolls Royce without the branding (so that I can do everything I want to it), Roll Royce should not forbid any other firm to build copies of Roll Royce's car, as exact as they can, but without the branding. ...
... For the same reason, I don't see why, after you bought a software, you could not copy it and give it or even sell it (but the buyer would be idiot) as long as you don't pretend you wrote it.