The "inifinitive" of the verb form apears like this: to be. It is grammatically incorrect to "split" the infinitive of the verb like this: "to just be." The correct way to write this would be either "just to be" or "to be just."
In many ways, this is an excellent example. "To just be" has a sort of Descartian ring to it - "I just am". However, it is a split infinitive. Unfortunately, the sentence "to be just" when taken in isolation means something very different - "just" would almost certainly be taken in its legal sense. It's a good example of the importance not only of clear sentence structure, but also of the need for robust word choice.
"To boldly go" is the most famous split infinitive (and, in my view, the only interesting thing about Star Trek). I suspect that split infinitives are now much less of a "no no" than once they were. A piece which is grammatically correct and well written would almost certainly be excused a split infinitive or two, but in a sloppily written or badly executed piece, they would just be taken as further evidence of poor writing skills.