Just because US law defines IP as an incentive not an inherent right doesn't mean that culturally it's only a incentive.
You have poorly defined what "ethical" means. So far the only clarification you have made is that legal and ethical are too different things. Some people disagree and define "ethical" as "law-abiding" which means that copyright infringement is unethical.
To be clear, I'm not saying you're wrong, I'm just saying that there is a degree of relativism to your statement. Just because you don't think that copyright infringement is unethical doesn't mean that people who do are wrong.
I'm not really a proponent of moral-relativism but ultimately I have to accepted that ethics are a human construct and as such disagreement will arise over its precise definition. For example, I think eating meat is unethical but most people don't. Does that make me wrong?