Because not knowing it creates an information asymmetry and makes it more difficult to make a rational decision about whether to pay for the product or service, or look/wait for alternatives.
It's not just about what the product or service is worth to me. It's also about a sense of fairness. I'm OK with a 20% markup on bottles of water at ball games. I'm not OK with a 200% markup, because even if I'm really thirsty, on principle I don't want to pay several times more for it than I otherwise would. So if I knew the exact margin, I can make an intelligent decision between paying for it then, or waiting X hours for the game to end so I can drink the water I have in the car.
I find that attitude a bit strange. Carried to its logical conclusion, you wouldn't want to buy a used car from someone if they received it for free, regardless of how much they're charging vs. market rates.
It makes sense to compare a product offering with other offerings on the market, but it doesn't make sense to me to care about the profit margin. What if one firm can offer a product cheaper than all equivalent competing products, but with a much higher profit margin?
The point I'm making is that a buying decision depends on much more than just the price you're paying. All kinds of information go into people's decision-making process. For instance, if you knew that the duck-fur coat (or whatever, I don't know if that's a real thing) you are about to buy was made by torturing ducks, you would be less likely to buy it, even if the price, by itself, was reasonable. This is why a lot of companies that sell animal products go to great lengths to keep such information from consumers: because the resulting information asymmetry benefits them.
The idea that at the end of the day the product/service is either worth it to you at X price or it isn't is simply wrong.
I suppose you have a point: if I thought earning profit (or a certain level of profit) was immoral, then I would want to know the profit margin before I made a purchase. I personally don't hold that moral belief, but undoubtedly some people do.
> Carried to its logical conclusion, you wouldn't want to buy a used car from someone if they received it for free, regardless of how much they're charging vs. market rates.
Great point. These objections to Instacart are not just bizarrely irrational, they are at odds with how the service economy works.
> makes it more difficult to make a rational decision
Your arguments are the opposite of rational though - and I'm not insulting you, I mean in the economic meaning of a rational person that just considers the cost and the benefit. Your arguments are irrational and emotional.
But I think you have a better argument that you haven't made clear - the markup gives you information in that if the markup is high then it is more likely that someone else is willing to sell to you for less if they can tolerate a lower margin. If a margin is very low then that's less likely, as there's nowhere to go.
