I mean you have to understand that we're talking about the more general application of ethics.

Killing a man is generally seen as unethical. Eating meat generally isn't.

So if a vegetarian was working as a taster for Al's Nothing But Beef restaurant, we wouldn't say they are unethical, but they are violating their principles.

Or if Stallman started working for Apple or Microsoft. He wouldn't be doing anything unethical, but he'd be violating every principle he stands for.

So I think the distinction is an important one. To separate one's personal principles from what is generally regarded as ethical.

I generally understand ethics to be relating to societal principals, whereas morals is more personal. It might be against a persons morals to violate their own principals (but maybe not, too).