If you're buying a used fork, you're paying for the use of the fork. If you want a disc then you can go to Best Buy and by a blank disc. But you're not....you're buying a disc with the software on it. The software is what you are paying for.
Hang on? For the
use of the fork? So I'm renting it? Nah. I buy the fork it's mine to do with as I please. Ownership is transfered and the previous owners has no claim or right to how I use it.
Software has too many grey areas over ownership, usage rights etc. It really needs to be simplified and put into less ambiguous language. Before digital distribution it was simpler. Normally I'll purchase a hard copy when given the choice. Once that's in my hands I'll use it how I wish. I've paid for it once, not paying for it again. EULA's are a mess, a largely ignored mess until aspects of them became enforcable. Now because there is the friction caused by the way that drm and digital distribution restrict what the end user can do as was seemingly the original intent large numbers of us aren't happy.
Second hand market is a good thing in my eyes, the publisher and developer have already been paid once for that item, if they want people to purchase subsequent titles then they need to accept not everyone is going to blindly chuck out £30-40 on a title when they can try it for a second hand price. If they like the title then chances are they'll purchase other subsequent titles, maybe even pre-order them. Treating the customer like scum because they won't pay top price is a good way to loose customers. In between lousy drm schemes such as Ubisofts always on or Steam as well as the general attempts to undermine the second hand market I can fully understand someone saying they've no desire to continue playing games if they're going to be treated in such a manner.
Are they lost sales? To the publisher sure. To the retailer, no. They're an excellent way to give more people the opportunity to play your titles and to increase your potential sales though. If the publishers are too dumb to see the long term advantage of the second hand market for short term profits then more fool them. Can't speak for others but when publishers pull mickey mouse

like Steam or Ubi's always on I loose any interest in the title or subsequent titles from that publisher. Flip side is I favour publishers like CDProjekt Red instead.
Other advantage of second hand is it allows you to find older titles that aren't readily available or that you might not have heard of.
All comes down to which group you're more concerned about, the publisher or the customer.