Well, you've already had one person disagree with you.
The only difference between an organisation doing it and an individual is the number of people. It is still illegal. And the fact that "a lot of people do it" (how do you know this?) and some are American's makes no difference. And how much the sales tax or VAT is also has nothing to do with it.
Okay, you don't like my stolen car analogy. But all I was really doing was determining how big a criminal you are, not whether you are one. Like the story supposedly attributed to Churchill (but some say Mark Twain): he approaches a woman and asks her, "Would you sleep with me for one million dollars?". She early responds yes. Then he says, "Would you sleep with me for a dollar?". The woman is insulted and says, "What do you think I am, a prostitute?" So he responds, "We've already determined that now I'm just trying to determine the cost."
But since the last person said they declared their purchases, and I don't know that most persons do it, then I'll amend my statement to be that we are supposedly "high and mighty" and at least one British person is a cheating smuggler through a lie of omission.
Of course I'm also assuming you've done this in the past? If you haven't, and this was all hypothetical, you have my apologies. But in any event what you are suggesting is a rationalization, and a poor one at that.