I guess people also are making purchases and signing up by mistake after clicking on ads. Just because you ignore ads, doesn't mean others do same. FB is already making profit on ads.
Clicks and sign-ups, leave alone purchases, are very different things. FB sells clicks, but a user just hits "back" button. Eventually, there will be no demand for clicks, because even being very cheap and abundant, they will not create enough money.
Profit = revenue - cost. So, FB pays all its costs from selling ads? Since when?)
Profit = revenue - cost. So, FB pays all its costs from selling ads? Since when?)