Of course, religion is about indoctrination. As a Christian, I am very interested in learning about the true doctrines of my faith and studying them closely. Indoctrination is only wrong when the doctrines are wrong! I plan on teaching my children about the truth of the Christian doctrines; I see no issue with that.
All religions use the same structure to lure people in to following it: Fear, unrealistic promises, facts that cannot be proven or refuted and eternal punishment or bliss. Somehow we all want to believe that there is something more out there because for the majority of us life just isn't good enough. It is the same as the myriads who play the lotto: In spite of the fact that your chances of winning is so minuscule you persist in buying one ticket after another in hope of winning the jackpot which, if won, will, we believe, change our lives for the better and make us happy. Owing to this religious salesmen (Priests, elders, rabbis, saints, popes, etc.) make a killing off "their" followers. With regard to it being indoctrination, my answer would have to be twofold: YES there is much indoctrination in the same way that most presidents try and indoctrinate their fellow countrymen into being patriotic but at the same time religion is what it is because human nature wants it to be that way and so inevitably we indoctrinate religion into indoctrinating ourselves in turn.
Religion is based on philosophical and mythological ideologies in which mass groups of people believe in some form of deity, higher power, idol or figure and engage in certain practices associated with their religious beliefs. Most people are taught from early children to believe in one particular religion which is mainly determined by geographical location. Children are very impressionable and vulnerable to brainwashing and religious propaganda. This is why it is so easy to persuade them into believing in mythological nonsense. This stems from centuries of indoctrination which is why it is so common but with the progression of science and technology, more and more people are starting to think logically about their beliefs and letting go of them.
Most people only believe in Christianity, Islam etc.. Because their parents and society told them that is the truth and they grow up and teach their children the same thing. It's a diminishing cycle of weak minded behavior in which people cannot think for themselves and make logical decisions. Many of them are also forced to believe that if they let go of their religion they will be severely punished in some way. Many of them will deny this but if they actually think about WHY they believe what they do, it all makes sense.
For example, if you are a Christian, ask yourself the following...
"Why am I a Christian?"
"Are my parents Christians?"
"Did I grow up in a predominantly Christian environment?"
"Why aren't I a (insert different religion here) instead?"
"Why can't I let go of my faith?"
These questions can apply to pretty much every religious person. Try it.
From the time we come into the world, our minds are constantly changing, manipulating and rearranging brain cells to shape our understanding of the world. And our first teachers, our parents, instill their back-boned values into us, so can we change how we view the world if we're merely impressionable and unable to think for ourselves? Do values from childhood stand the test of time in our changing world? Yes, they do, and it all begins at home--by manipulating how we feel, how we think, how we act, anyone can sew any idea into our beliefs.
Religion is the act of believing in a god, and worshipping him, not to deceive others into believing what you wish to believe. Many religions do not even recruit other members, and they especially do not trick and brainwash them into doing so. The only ones that do are cults, and those are not proper religions. Christianity, at the very least, is about god, and life. Not about brainwashing or deceit.
It's pretty ironic that the people who call themselves "free-thinkers" think that if you don't think a certain way that you aren't thinking for yourself. Free-thinking means that you question things and come to your own conclusions by thinking it through. The conclusion doesn't matter. Atheism is not a byproduct of questioning things. Indoctrination does exist but the vast majority of religious people are laissez faire about religion and allow you to question the religion. So by definition it is not indoctrination. Sorry, Not sorry.
Religious belief is passed on through indoctrination. You ask questions when you are young, and you are either given non-answers or pressured into not asking them, forcing you to simply reason illogically or accept things dogmatically.
But this isn't the whole story. Consider why people often return to the church after having kids - a huge part of religion, and likely the only real utility to it as far as I am concerned, is the community portion. Churches generally provide a communal support structure, a reason to get together and engage harmoniously, and come together in times of need to support people in the group.
So yeah, indoctrination is a big part, but there are other driving factors to people being religious.
If it was just indoctrination, we would never have had a church, as you would have had someone to indoctrinate the indoctrinaters - circular argument. Instead, it seems far more likely that, while there is a huge component of indoctrination in any religion, that the lack of answers for the big questions, the lack of ability to accept large unknowns, is also a massive driving factor.
It depends on how you teach the religion. If you teach your kids just your religion, and nothing else, (such as other religions, government, etc.) and use fear as a tool to get them to obey, then I would say it is indoctrination. So no, religion is not SOLEY indoctrination.