Re: You can not to go there!?
This question is obviously trickier than it seems.
"You can go" (versus "you MUST go") already has an option of "not going" built into it. You can go if you want, but you don't have to.
So the opposite, in my opinion, is "you cannot go."
If you asked about the opposite of "you must go" it could be two things. Is the "opposite" of an obligation to do something a) The OPTION of doing it (or not), or b) The prohibition against doing it?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.