I feel like there is a bit of ethical hysteresis here. If you have buttons that are designed to be placebo from the start, I find that unethical. If you have buttons that work, but have to be disabled due to a change in plans, that strikes me as less problematic (but they should still eventually be removed). So, how you get there matters.
Is lying to people for their own good ethical? You decide, I don't think there is a correct answer.
In fact the second case (not removing the buttons) can be seen as the least ethical of the two. In the first case, it is an assumed choice, you did it because you think it is for the best.
In the second case, you let money guide your ethical choices. That's essentially Black Hat's answer to the trolley problem (https://xkcd.com/1455/)