I find it hard to feel strongly about anything these days. But I still feel, in a sense, outrage when I think about some of the things that religious people are allowed to do. I think it's a fine thing to be religious, and I think you ought to have the right to do with yourself as you please (as long as it hurts no one else etc.), but when you force things onto to children, who probably (maybe not in the case of child geniuses) cannot give consent - not that consent would matter in this case as you'd force them into it anyway - you are impacting heavily on freedoms you would strongly defend if it were you in the place of your own children. I will provide three major examples: Indoctrination, Circumcision and Fasting. All three of these violate the consent of the child, and two of them cause suffering from the outset.
Indoctrination annoys me quite a lot. Not only because it creates yet more zombies hellbent on procreating this world into a nest of ants, with each of us crawling over one another to get by, but because having a religion is a sufficiently large enough decision that indoctrination will always be felt as a breach of rights. You may argue that parents can act 'by proxy' to consent for their children, but in this case doing so easily allows cults to spread, and for children to suffer nightmares from visions of hell and such. Clearly since this involves suffering, consent does matter. Is it not better to simply wait until the child is older to let them decide about matters of religion? Also consider a person forcibly brainwashes you into believing in his or her religion. Would you not protest against such a thing happening? Why don't you stop the same thing happening when you do it to your own child?
Circumcision is pretty easy to argue against: if someone held you down and cut off your earlobe, without anaesthesia, would you sue them? Is that clearly not assault? Does the consent by proxy argument work here? No, because clearly this is a matter that brings real suffering and is completely and utterly useless. If a parent can consent to circumcise their child, then a parent can consent to mutilate their child in any way they want as long as it heals eventually and doesn't bring lasting harm. Even if it brought no suffering, the fact that it can go wrong, and little boys can suddenly find themselves becoming more like little girls overnight, means that something for little to no reason can result in life-changing consequences. It's okay to get circumcised later on in life of course, and I don't see why a religious delusion has to be upheld like this just because we're afraid to step on a few toes.
Forcing kids to fast is something a lot of atheists don't address, but which annoys me all the same. That's the same thing as forcing them to suffer - for little to no reason at all, again. It is DIRECTLY forcing them to suffer, as constant hunger is exactly the same thing. As with all these things, it is barbaric - a relic of times when people had to show in-group loyalty fiercely as food was scarce. The nomadic Abrahamic religions' cruelty I suspect can all be traced back to these conditions.
Don't mutilate your children, don't let them starve, don't brainwash them, and don't sacrifice them for a good harvest next year. Be religious, but remember that greater powers than your imaginary beings should bind you at all times.
EDIT: Think I was wrong on the indoctrination part - it's committing harm because you're forcing them to believe in scary lies, but not forcing them to believe in barbaric rituals could also be considered a harm. It's a Catch-22 situation. Indoctrination is bad only if a scientific study proves religious from birth happier than atheist/agnostic from birth.