Being forced to and what you will do are both "have to" Kusanagi-san. If that's the only option you'll think about, it may as well be the only option.

[...he hates this. He knows exactly what they're talking about now, just not directly and... For the clan, it makes sense that Izumo would be the one to remain behind, should be the one to remain behind, but. The three of them started this. The two of them took Mikoto's hands together.

He knows what'll happen.]

...what about Anna? [There's no use pretending he doesn't also know how this'll end for him anymore.]