Developers/publishers don't have anything against the 2nd hand sale of their product per se, this was happening for damn well years and decades.
What people don't understand is that they're not hating on the customer trying to maybe sell a game to a friend (or give it to him) for a very low price or people selling them on eBay or similar, but that there's an actual problem in a parasitic industry living off the game sales and increasingly devouring more and more of their profits at near to no personal risk whatsoever... impact of which is that they open more and more stores/branches to make even more money, and upon seeing how much success (GameStop) is having in about ~30% of their total profit (being pure profit) coming from used sales and the rest from hardware sales and "other" (which would indicate that used game sales equal upwards of 40% of their total game sales taking hardware and other gadgets aside), other major retailers like Walmart, Amazon and BestBuy are already following suit with more to surely come if the developers don't do anything, united and fast...
Lowering prices won't work, as has already been stated some games DO lower their prices rather quickly (especially in Europe... can't say it for the US, but we don't really have that much of a problem with big-ass retailers fucking over both customers and publishers at the same time here) as said retailers will just lower the demanded buyout and sale price somewhat and be done with it... If they're buying the game for 10-20$ used from someone and either sell it for 45$ or 35$ won't make that much of a difference, as apparently the 5$ difference compared to an actual new product (not enough grasping the point of view of morality in actually wanting to reward developers for making a good game and making sure they do more of them in the future) seems to be enough to entice enough people to grab that copy instead of the "new" one anyway and they STILL make a pure profit of 15-35$ at almost no personal risk or additional costs.
Publishers simply cannot compete with them in any way, seeing as they are the ones paying for the actual game to be made, the marketing, salaries, shipping, legal fees and so on while carrying the risk of a game totally backfiring and flopping not even covering their expenses at the same time while all GameStop has to do is buy a product cheaper and sell the same one at a higher price being able to analyze how good certain things sell and how profitable they'd be bought and sold at a certain price... they're NOT in the same market to be able to compete with each other, so unique keys for each copy (especially the ones with an online component) or a service like Steam are really the only ways to go for them.
As I mentioned before in other threads, "used sales" are actually a lot worse for the publishers in a financial/business sense than piracy could ever be, because the consumers buying a used product indicate that they want to spend money on it (being it 5-10$ cheaper) and actually do it, while pirating something for free will not equal in actual money being transfered and lost to them.
They might even be willing to offer special deals on their games or sell them for a lower price after a time or on special occasions (leaving Activision Blizzard aside, they're just batshit greedy) like they already do with their Steam sales or special prices over the Internet, but there is no way to do that with retail products and a chain like GameStop would still be able to undercut them even then using their "unique business model" of screwing both customers and publishers.
Furthermore, buying software used (especially games) has nothing in common with buying a used TV, car, dishwasher or "whatever" WHATSOEVER.
While there is some software that you'll buy to keep it around, like say Windows, Office or Photoshop you will probably need for working and using it long-term, games are just largely throwaway entertainment products most people play through once (often offering only 6-20 hours of fun) and then either chuck them in a corner or reselling them.
THINK ABOUT IT, 1-2 days after the initial launch you will be able to get used copies of said product cheaper than its original price, and that "launch time" is mostly the only time said developers and publishers will see any money out of their product...ever. You do not buy a TV, car or dishwasher to use it for a day or two and resell it again, and there's always the fear that you'll buy something that will break down soon, is of bad quality or out of date and might need a lot of repairs (where the original dealers usually still make money) or is plain unsanitary when you buy those used that can be omitted from software sales.
You could compare it a lot more with movie and music sales (although both books and music albums take nowhere NEAR the amount of effort, manpower, money and risk it takes to create games), but as has already been said... you can actually pay dozens of different ways for those, buying a one-time-one-person-only theater or concert ticket to watch it once or several times with different people, buying said CD/DVD/BluRay a few months after, paying your cable/radio provider that pays for the rights to the movie for PayTV or watching it with commercial breaks on FreeTV, buying mp3s or movies from Online retailers like iTunes, renting them etc. etc.
It's not the same thing, and chances are said game even cost a lot more to produce sometimes.