Possibly not unpopular, but it was an idle thought that occurred to me yesterday.
Why should I have to pay 30¢ for lettuce when I let you keep your mustard? I’m reducing your costs. Or if I take pickles off your baseline burger, you should reduce its cost by that 30¢. It’s the principle of the matter.
Some McEmployees understand how the “substitute” function works, but many don’t. I understand that you should be in the ballpark of similarity for what you’re asking, but if they don’t already understand the concept it’s just not gonna be worth trying to explain.