Yes, the State was not improper when it prosecuted Scopes for teaching evolution. If it were the other way around, and the State made a law that it was illegal to teach creation in school, liberals would certainly want prosecuted anyone who did. I disagree with the law, but if it is a law, there is nothing wrong with the State enforcing it.
The idea that we should teach children the truth has an inherent flaw. Teachers cannot be expected to know what truth is. Since our understanding of the world, social context and human experience is ever-changing, it is a losing proposition to teach absolute truth to children.
Rather we should teach children how to think. By teaching evolution, or creationism, or any other origin story, we present the idea that a single truth is known and accepted. This ill-prepares students for a world in which many different beliefs are held by different people groups. It would be better to teach all of the known philosophies, theories and hypotheses held by a significant population, and educate students on the existing debates and the arguments presented by each side. This would not only allow, but encourage students to make up their own minds when presented with conflicting viewpoints.