What's wrong with FREE jobsites?

There has been a spate of "on line industry experts"  denigrating job boards that offer a free option.  It undervalues the industry they claim.  I wonder what Reed would say to that, having spent the vast majority of it's existence as a free site, now reportedly the UK's most popular site, and certainly offering a service of considerable value?  Do these people not then take advantage of BOGOF or other  free offers in the supermarkets, seeking out the most expensive item on principle? I bet not!