The issue is even without conversion, they will still raise their kids instilled with unfounded beliefs as truth. In my mind, this severely handicaps the rational thinking ability of these children, I know it did to me.

Growing up thinking I was going to go to hell for who I was crippled me with severe anxiety that still affects me to this day because it happened during my developmental years. I had nightmares for years about being torn apart in firey depths by demons. When I woke up I would remind myself that this was just reality and I should just try harder to "fix" myself to not be a "sinner". Knowing now that it was all lies fed by my parents to control my thoughts and behavior makes me unspeakably furious and resentful, even though they were not doing it to hurt me.

Even without wars between religions, they are incredibly harmful to the some of the people that believe them.