Thank you for the good question.
As for the study of the main religions, their sacred writings/scriptures and the history of the religions and the scriptures, the answer would be positive only on condition that:
1/ Teaching and textbooks are objective and not aimed at proselytising;
2/ Students are old enough—for example, in high school;
3/ These classes are optional—on this complicated matter, it is supposed that there will be parents who will not want their children to study things objectively.
Unfortunately, this endeavour will stumble at inception. Who will prepare these textbooks and teachers? Atheists? Christians? Muslims?
I will give an example I encountered a decade ago. Since the fall of the socialist regime in Bulgaria, there had been a great debate on this subject. The idea that children should study Christianity prevailed. For this purpose, textbooks were written (translated from Russian).
Here, I will only mention one that was intended to introduce the youngest students in the Bible. It is called “Bible for Children,” and is intended for ages 8-11. Of course, it was endorsed by the Ministry of Education.
It transmits the biblical message in abridged form following the real sequence of the most important biblical books. Immediately after the fall of Adam and Eve, you will read the following text, presented in the same font as the natural paraphrase of Genesis:
“But God did not cease to love people. He promised them that after many, many years He would send to the earth His Son Jesus Christ, Who will take all human sins into Himself. He will become the Saviour of mankind! And everyone who loves Jesus, after his death, will go to heaven to always be with the Lord.”
The chapter of Cain and Abel in Genesis starts with the birth of Cain, whom Eve dreamed of becoming great and powerful… “Then, his son shall also be born, who shall also have his own son, and thus, after many, many years, Jesus Christ, our Saviour, of whom God spoke to them [Adam and Eve], shall be born. Eve dreamed of it when she put her child to sleep. And after some time, Cain’s brother was born, and they named him Abel.”
Sentences / sermons about Jesus are also interwoven in the text of Noah and the ark, the story of Abraham, and so on. In short, the entire Old Testament introduces us to Jesus and his mission.
(This textbook has been in circulation since 1993.)
Sooner or later, these children will understand the truth about the so-called sacred scriptures… And the moral responsibility of those who manipulated the meaning of the message is great. If such interpolations had worked from the 1st to the 19th century, then, in the age of information, they would have only a perverse effect.
So before we vote on whether religion is to be taught in schools, it is better to ask ourselves if we can provide unbiased professionals and study materials. (In fact, this concerns equal representation of all major religions, not just one.)
Unfortunately, my answer is that we are not yet ready for that. (I am pessimistic we will soon be.)
Indeed, in the last ten years, books have appeared that are more close to objectivism in revealing historical truths about religions and their “sacred” writings. New archaeological discoveries can also help the topic of religions / scriptures be presented objectively. But this probably would be for history lessons rather than religion.