If religion is the free service of superior supernatural beings or a God then Humanism is not a religion for it is a sensibly selfish and Atheistic system of philosophy and denies free will. Humanism is practical atheism, it means living as if there is no God and seeing that nobody has the right to give you orders in the name of religion, in order to put oneself and others first.
If religion is trying to live in harmony with the powers that you believe is in control be it God or just chance then Humanism is not a religion for we don’t really care why we exist or how but just worry about how we are going to live. We do not live in harmony with our worldview but each person lives in harmony with her or his own psyche and any harmony with the world is just a side-effect. Some sects believe that God is so good that he doesn’t care what we do and will still let us into Heaven and they are undoubtedly religious though this definition would say they are not.
If religion is devotion to a moral ideal then Humanism is not a religion for there is no free will so there is no morality. Our living caring lives is no more religious than a clock ticking. We know that what is harmless is not immoral but most religion bitterly opposes many harmless things. Any religion that does that has no right to be called a religion. It is a cult. A cult is a religious system that abuses its members.
If a moral ideal is what religion is then every kind of group must be a religion even a maths class!
If religion is that which tells you what to believe and do then Humanism is not a religion for it does neither. We just present the truth and say what reason says. Advise others what to do when they want to hear it but remember they are meant to ponder on it and reject it if they so wish so avoid commanding and patronising. We all do wrong so we cannot demand that others do what we think they should do for that is egotistic hypocrisy. Demanding in the name of God makes no difference because that means you are trying to impose your perception of God and his ways on them - one of hundreds of reasons why there is no value in believing in God. If you have to give advice though you don't keep it then get it across without making it seem that you consider yourself perfect and in a position to be condescending.
If religion is faith then Humanism is not a religion for it gives knowledge.
If religion is just your deepest concern then Humanism is not a religion because the concerns we have are not ours but the product of blind natural forces.
We are concerned only with unspiritual things. Spiritual means following the principles of and giving allegiance to higher beings like gods and spirits while all we Humanists care about is feeling good which is totally materialistic and earthy for it is material forces and energy that give us feelings and happiness. Spirituality is not religion though you can't have a religion without spirituality. Religion seeks help from outward occult forces while we do not so we are not religious.
If religion gives your life a meaning then Humanism is not a religion for there is no need for religion to feel your life has value and Humanism asserts that firmly.
Whatever good religion can do, we can do better for religion thrives on egoism and egotism anyway so when we are egoists we can cope without it. Religion can only work if it recognises that the only person who can make you happy is you but if you have the knowledge of how to achieve this then what do you need religion for? Nothing is the answer and religion can only get in the way for the best way to get to the goal is to go in a straight line to it. Religion is intrinsically cruel and it is arrogant for any religion to claim to be the true religion or to follow a man who is the only way to God. When you say your religion or saviour is the only way or the right way to God you are boasting that you know it all. The person who tests all things by pure reason alone and who embraces only what is reasonable can say that she or he is right.