Why would they be able to charge more for something people don’t want?

Psychology. People have an inner understanding of how much things "ought" to cost. If you charge more than that, you need a differentiator or it will trigger their scam detector and they'll reject you.

3D is a good differentiator, and allows for a price raise that otherwise doesn't appear justified.

Ok. But if people prefer the 2D version, then they’d not pay more for something they like less.

Actually yes. As a commenter above me hinted at, you would if it was the only option you had. I had to see ep 7 in 3d because there was no 2d showing on release day.. But I'd rather pay a bit more and watch it in 3d than to not watch it at all

If it's the only option you have they could just raise the price without implementing 3D. After all, ticket prices have risen over time for the same formats. Of course, the reality is that you always at the bare minimum have the option to just not go to the cinema.

No not quite. The thing is that they have a normal mix of 2D and 3D showings but not on the release day. So the issue is of wanting to see it the first day. So they have the normal division of prices between the two of them, but you are essentially forced to go for the more expensive one if you want to see it when it is released.

But you still have a choice, which is all I was saying.

Well true, you have a choice in everything. But given the constraint that I want to see the movie on release, my choices are more limited.

Because in a lot of markets they control the supply. 3D provides leverage to increase revenue across the board, and if 3D is the only option to see Star Wars, people will choose to pay more and see it in 3D when faced with the option of not seeing it at all.

Because the people who do do are willing to pay more.

That’s my point. People do like 3D movies. Not everyone, but enough to dedicate screens to it.