They tried to sell cheats.
edit: All right, let me see if i can't elaborate a little on my views of DLC.
I don't like spending money. It's more tolerable for me to spend it in one chunk than to spend the same amount over several transactions. (I'll get back to season passes in a moment.)
I like costumes and items. I do not like buying costumes and items. Every time, i will choose simply to go without them, rather than to make another financial transaction. When it's cheaper to forego colorful costumes, why wouldn't i? I can buy a delicious grinder full of meats and vegetables with that money. You want me to give it away for a trinket in a game? I buy games for their engagement value, for their entertainment, and i can get by without a slight variation on a shotgun.
When a game is constantly badgering me to spend money is the worst. It utterly ruins the relationship. Art, engagement, entertainment, exploration -- anything i get out of the experience is taking a back seat to capitalism, as the developer has prioritized it.
I don't like buying missions, but since they're a substantial chunk of "actual stuff", i can tolerate it a little better.
Season passes are asking for more trust in the quality and value of vaporous futures than Volition has earned. I'm not sure that any company has earned that level of trust from me. Maaaaybe Valve, but they don't pull DLC shenanigans like this and have not yet tried "season passes".
I oppose DLC in general on two more philosophical points, related by a common cause: division and overhead.
Division
As soon as you publish DLC, you separate the players into the "haves" and the "have-nots", so some people simply aren't getting the same experience as others. I have an instinctual distaste for that, and i don't think i can really explain why. Although it might have to do with the fact that if you play a DLC-laden game, and your friend plays it a year later, your friend experiences a better game that cost less. That hurts.
Overhead
DLC requires accounts. I know you're publishing exclusively on Steam, which means you require accounts anyway. Still, having DLC means you never have the option of a DRM-free release, and other games suffer for that. I see this as unnecessary tie-in to a fragile system that might not be there tomorrow (something like, say, GFWL). I actually don't know how CDPR handled DLC for The Witcher series. I'm pretty sure TW2 had some, though it was made free later.
And they tried to sell cheats.