I mostly agree with you and Google has already been accused of mixing paid listings into their search results. However, it seems that search engines are really sensitive to being labeled with this stigma. If this becomes common practice again, then it opens the door for someone else to be the new Google.
they are never useful or informative.
He/She seems to be referring to advertisments in general, making the statement all the more ridiculous. Advertisements are one component of marketing, and without them, all the other--more dishonest--components have all the more power. Most prominently, advertising allows the smallest companies to compete for attention along with massive companies, if only in a targeted way.
identifying ads is relatively easy technically
Oh, you think so? Well, when adblockers become standard issue, I can assure you that advertisements will be very difficult to identify, because they will be incorporated into search results, as in the old days.