“I was only following orders!” This classic statement has been used by people throughout history to justify immoral and unethical behaviour. The question is whether or not this is a viable excuse in our daily work environment.
Clearly a senior executive has the right to make decisions and to expect those decisions to be followed. I would even say that a senior executive has the right to have wrong decisions followed. Occasionally, I find myself in discussions with colleagues who are frustrated because of a poor decision made by a senior manager. Sometimes my advice to them is simply to implement the decision (after first having done your best to point out the why the decision is a poor one). The fastest way to get some managers to realize that a decision was wrong is to actually do what they say. You might never get that person to see their mistake by arguing, but it will be very clear once the decision is implemented. (Who knows, it might even turn out that the decision was the right one.)
What happens if a senior executive insists that you do something that is either ethically wrong or possibly even illegal? The simple answer is that if you agree to do as this superior says, you are accountable. Morally you are complicit in the action which has been done. You are equally guilty if you see unethical behaviour and do not act to correct it.