I guess I don't understand where you are coming from. In IL for example, has the separate test to practice structural engineering in IL which is totally separate process from the PE. So unless you have to experience to back them both up, they aren't interchangeble. for other states that might be different
i am from Illinois, that is where the unfairness come in. People who pratice SE almost 100% can apply to take PE. However, on the other hand, for example, I have a degree in electrical. My education background totally stop me to take SE exam.
So, it is only fair if people have background in Civil go to take SE, while other take PE.
With only Civil can take both SE and PE is extremely dislute the value of my PE licnese.
I'm not sure how all states handle this, but Washington does not explicitly require a Civil license to take the Structural exam. What it does require is that an applicant must have at least two years of Structural experience. It just so happens that small-scale structural work (ie that which a non-SE licensed individual can do) tends to fall under the "Civil" engineering category as a general rule. But, there is generally nothing in any state preventing you from acquiring a Civil license - if you can pass the exam. And if you can't pass the Civil PE exam, you probably have no business even thinking about taking the SE at that time - most of the engineers I know consider the Civil PE is a cakewalk by comparison, to the point that one of my coworkers has had a Civil license since 1998, done almost exclusively small-scale structural work (including medium-size concrete structures literally a foot under the SE-required height and less than 100 s.f. under the area requirement), and still doesn't consider himself ready.
Generally, any state allows you to "jump" from one license to the others, once you have proven yourself competent and ethical in one area. I'm planning on getting my SE, EE, ME and Geotechnical licenses that way - I have my civil, so (except for Structural) all I need to do is pass the other exams.
Keep in mind SE is (well, in OR/WA at least) only required for a certain height (45'?) and area of structure, or for important structures (schools/emergency services), or when the building dept wants to request one due to a specific situation. And even then, some jurisdictions allow exceptions via building official approval.