For many religious people, raising their children in their faith is an important part of their religious practice. They might see getting their kids into heaven as one of the most important things they can do as parent. And certainly, adults should have the right to practice their religion freely, but children are impressionable and unlikely to realize that they are being indoctrinated into one religion out of the thousands that humans practice.
And many faith traditions have beliefs that are at odds with science or support bigoted worldviews. For example, a queer person being raised in the Catholic Church would be taught that they are inherently disordered and would likely be discouraged from being involved in LGBTQ support groups.
Where do you think the line is between practicing your own religion faithfully and unethically forcing your beliefs on someone else?
Each teaching has to be evaluated on its own merits, its basis in reality, and its effect on the child and how they relate to others. Whether it’s religious in origin is ultimately beside the point.