There are a lot of Christians out there who object to the teaching of evolution in public schools. They want the subject removed from school science texts because they believe that the subject undermines True Christianity. Other believers argue that there is no conflict between religion and evolution, so it should be taught. Few if any secularists think that the presence or absence of conflict with religion is relevant -- so long as it's science, it belongs in science classes.
Quite a few people fall for the "teach both sides" argument because it has the superficial sound of fairness about it. If there is disagreement, why not tell kids about both positions and let them make their own minds up. This might make sense if the disagreement in question were a matter of legitimate scientific debate, but there are no scientific grounds for disputing evolution -- there are only scientific disagreements about some of the details.
William Jennings Bryan At Scopes Trial
It is also questionable how many kids would really be in a position to seriously weigh both sides and come to a sober, objective conclusion. It's far more likely that creationist parents would use the situation to further impress upon their children an anti-science and anti-rationalist perspective which fits with traditional superstition, but which is incompatible with modernity. Even worse, encouraging such ignorance and anti-intellectualism is touted as a "family value" in some circles.