You will not be obligate to play it if you dont want to, they said that they will finish the game for single player first with at least the same content than witcher (2 DLC) and maybe after they will add it so i dont see where is the problem.
I m sure i can have lot of fun with friends in the game like in red dead redemption or gta, i dont want special game mod or wathever, just chill with friends in the free world is ok for me (if youre afraid about the time devs can spend on various things that i for exemple never played in gta..)
For me there isn't a major problem, I'm getting the game either way, but the "problem" (minor issue) for me is that between my job, family, & social life outside of gaming, I only have a few hours a week to play. Sometimes I want to murder some fools with my friends and jump into a multiplayer game of some sort, other times I want to be alone and just experience a narrative, get lost exploring, just to play on my own terms. If my single player game has multiplayer options, then when I choose to be alone my friends don't know that, I start getting invites/messages, and then I either feel guilty for ignoring them or compromise my experience and join. I'm going to be disappointed with either choice which I'll only be able to make after spending several minutes in a neurotic argument with myself.
I get that many gamers have a ton of alone time that they can use however they want, I get that I'm probably more misanthropic than most, and looking at trends in game I know that I'm in the minority for not wanting a game with both options, so it won't bother me if it does have it, I'd just much prefer it if it didn't.