Asking about the value of ads is like asking what value I derive from buying gasoline at the petrol station. None. I derive no value from it, I just spend money there. If given the option between having to buy gas and not having to buy gas, all else being equal, I would never take the first option.

But I do derive value from owning a car. (Whether a better world exists where my and everyone else's life would be better if I didn't is a definitely a valid conversation to have.)

The user doesn't derive value from ads, the user derives value from the content on which the ads are served next to.