Why not? When I was in school, those earlier ideas WERE discussed. One can easily see what “theory” the evidence supports, and reject the ones that aren't supported!
(Or is that exactly what you fear?)
Why does this need to be taught in the school? Like it or not, creationism is a religious belief and schools are not in the business of teaching religious doctrine. If parents do not want their kids exposed, they can home-school their kids or send them to religious schools.
IIRC, the Texas standards apportion only 3 days to evolution. That sounds about right; when I took biology in high school, it was a very, very broad survey course. We didn't have time to debunk every proto- or pseudoscientific "theory" from history or modern fringe groups. If we did, we never would have gotten through the first chapter!
Same thing in every other class. We didn't do celestial spheres in Earth science, the Fomenko chronology in history, or homeopathy in health. There are only so many days in the school year, and only so many tax dollars available for education, and school boards must be good stewards of those resources. High schools should present students with the current state-of-the-art of science, not bog them down with earlier, rejected theories and outright junk science. There are college-level courses that specialize in that.
In gradeschool science, I remember discussing (and rejecting) theories of “spontaneous generation”, which is life from non-life (you know, like molecules to man).