You hit the nail on the head. If it is per impression, then yes, there is some information they would like me to have and there is some profit that this site is receiving from those impressions. It is fair game then to have me see those ads if that is what the model is as long as this model isn't abused.

If the pay-per-click is supposed to piggy back on free impressions then I have zero conscience of denying them free advertising.