Why is the theory of evolution taught in schools (In America) so furiously and relentlessly? ?

I always thought it was the something accepted or something that just happens because teachers told you so. But of course, this kind of life style will lead you to death if you believe everything you're told. One day I watched some TV program talking about how dolphins turned into dogs. At first I was skeptical because It didn't seem plausible, and from there, that's when I started researching further on evolution. Then I realized, that if you believe in God and creationism, you cannot believe in evolution. The two ideas contradict each other, but I also realized that so many religious people out there are taught evolution, believe it, yet they live on without even thinking about how it directly contradicts with their belief. Why is this so? Why is evolution taught in every chapter and every section of our science books yet they don't even mention that it directly contradicts the religious idea of creationism (which so many people believe in). I know that there has to be separation of church and state, but couldn't our education system mention that the theory of evolution is indeed still a theory? My best guess is that perhaps there's political conflict amongst religious groups and many atheistic biologists. But of course, I'd appreciate if there was someone who could further explain the situation along with their own personal opinion.