I don't mind DLC when it's meaningful. Thing is, I like to aim for completing Achievements; it's something fun for me to do. I like to have things completed when I can. So, when games add the DLC Achievements to a game, and they're on your record when you don't even HAVE the DLC, it annoys me.
However, that's not what would keep me from buying Horizon, it's just one of the negatives. The thing that really gets me is WHAT YOU GET for that $50 Season Pass on Forza 5. You get 60 cars...why? I mean, that HAS to be the biggest rip-off for DLC ever, IMO. They take the 500 cars in Forza 4, scale it back to 200, then add just 60 for another $50? For $110, you can JUST get past half the car count of the previous installment.
If they were doing something like a quarter per-car, or $25 for 100 cars, I could possibly live with it. However, nearly a dollar per-car is such an outrageous price, and I can't stand it.
Personally, my lifetime DLC purchases on console are pretty small. I think I got the Halo 2 maps, one Halo 3 map pack, and 2 songs on Rock Band 2, so it's maybe $50 total. My typical response is to wait for a GotY edition of a game (like I did with Borderlands 2), THEN buy the game with its DLC.
I don't think DLC needs to disappear, but the business model is terrible. $50 for the CoD Season Pass is wretched. At least Watch Dogs and Titanfall keep it to $20 and $25, respectively.