When is Illegal NOT Illegal?

I have started writing this post a dozen times only to stop, each time realizing I was in conflict myself, however after much thought and pondering I realized there are some basic issues that should be, well... just basic...

1: If you are in this country Illegally you are breaking the law...

2: If a police officer has cause to detain you what is wrong with determining if someone is in this country Illegally?

3: What part of the US Constitution is violated if a police officer asks for identification and proof of residence?

4: Who in their right mind would allow Mexico to challenge a US State Law, passed in that state and applying to that state only?

5: What part of Illegal isn't Illegal?

Pretty simple when you come right down to it...

-Bob