Why do people have such a difficult time grasping "the sex you were born as" creates just as many problems as "the sex you identify with"? Again, I go back to Shawn Stinson.
Do you want this person in the women's room with your mother? Because that's what your "solution" (and HB2) suggests.
What makes a hell of a lot more sense to me is going into the room that corresponds with your appearance (see also: common sense or...what happened before NC started any of this nonsense). Sure, that leaves open some gray areas where people's interpretation of how "convincing" they are is debatable. But doesn't that exist regardless?
That's the dumbest part about the whole policy. Like you said, it affects a small number of people. It's a non-issue being dictated with non-solutions. And to think this was brought forward by a "less government is the best government" group makes it even more laughable.
As for your McDonald's analogy...you might want to read up on that case too.
http://www.lectlaw.com/files/cur78.htm