I don't feel like it's wrong but when you buy a used game all the money goes to the store instead of the publisher/developer.

If the games are still available as new i try to get them new.
But if i need another copy for CoD:MW2 because the disc broke I get it second hand

Nope, cause the publishers will fuck us up in other ways... Like DLC and Season Passes and other nonsense... If the publishers don't want used games, than make games that we don't want to trade in!

Agreed, because of that I never buy used games, unless is a game I sold in the past.

Yes. Especially if you are a Nintendo Fan. Nintendo needs all the money they can get. We need to help them in a time of need.

Personally though, I buy all my games new. It's an OCD thing with boxes.

It's not wrong to buy them. Its wrong to sell them in the first place. I mean why would you? Just because you need money? That's a bad reason for selling your kids.

I tend to avoid the practice. However, if it's a really old game that has already gone on to be a success, and the used version is significantly cheaper than a new copy, then I'll go for the former.

Yes, keep buying used games. So I can get a reasonable trade in value to finance new game purchases.

The publisher/developer already got the money for the game from the first buyer.

Many wouldn't buy a game for full price without the option to resell it, others wouldn't (or can't afford to) buy it for full price, so they buy it used. Without the combined revenue of these two groups, less units would probably been sold at launch... some would cave in and buy for full price, but many would just wait for a price cut... or wouldn't buy the game at all.

Publishers/developers can get something extra if the buyer of the used game buys some DLC additionally. 

Not at all.

Used games are legal.