The reason for keeping long hair is as a constant flag of one's religion, established originally in an India of forced conversions and religiously oppressive invading rulers. It is not, as commonly claimed, because we should leave our hair untouched because that is how we were made by God.
There are several contexts where hair is mentioned in the Sri Guru Granth Sahib, but none of them remotely suggest that cutting hair is somehow defacing the body given to you by God. Guru Nanak and other authors criticize specifically those that pluck hair out of their heads or the shaven headed ones, but they are referring specifically to Jain monks and use this to identify some of the things they disagree with in Jain philosophy. The similarly criticize Yogis who keep long hair, but allow it to become matted and dirty. The only favorable descriptions of hair are of it as being clean, well kempt and oiled, and beautiful. Occasionally in metaphorical descriptions of God, he is given as having beautiful, clean long hair, but the emphasis here is on beauty, not on hair. The gurus abhorred keeping rituals that were painful or purposeless and this is the only context in which the way that people keep their hair is mentioned in the Sri Guru Granth Sahib.
In my reading of SGGS, I see a few basic principles that lie behind the restrictions commonly associated with Sikhism. I consider these principles to be far more important than their manifestation. These are the two that I believe apply to the discussion of kesh:
1) One achieves unity with God by achieving harmony with the universe as God is all-pervasive and we are all connected to God and all of creation. All of us and all pieces of creation have a role in the Hukam and only by fully using your abilities and talents, and only by truly following the desires of your soul, can you fully fill the space you are meant to fill. But in order to fully use your abilities and talents, you must not harm your body or mind, the tools that you have to live the life that will bring into true communion. Therefore, Sikhs are not allowed to drink, smoke, etc and are discouraged from ascetism and other deprivatory or painful religious practices. Jains are criticized for having no hair, in part because it was a practice of the religion to rip the hair out of the head. It is necessary to maintain the body and the mind, just as it is necessary to maintain the soul. And in the vein of maintaining the body, hygiene is routinely emphasized in the SGGS. Yogis are criticized throughout the SGGS for having unclean hair. Living in harmony with everything else, living in the Hukam, means that you must not harm or disrupt the balance of the universe around you, but rather work in tandem with it. Thus Sikhs should not take more than they need and should not harm others.
2) If one claims to be a Sikh, one should be willing to stand up for his/her beliefs, should not hide his/her religion or be ashamed of it, and should be willing to die for the freedom to practice it and for the freedom of religion in general. These are the reasons that long hair became a mark of the Sikhs. Because of the ****** history faced in the early time of the religion, during the progression of the Gurus, it became the practice of the Khalsa, all of those who claimed to follow the teachings of the Gurus, to keep their hair long. It is one of the 5 K's that a Sikh is given to wear. Long hair is so that a Sikh can be easily identified, and another is a comb, symbolizing the cleanliness and hygiene expected of Sikhs. In a time when proclaiming a religion different from that of the Muslim conquerors of India could earn you death, it was a matter of pride in one's belief and of standing up for freedom of religion to keep one's hair long, clearly wearing one's religion for everyone to see.
So how does long hair apply to these principles?
Cutting one's hair does not harm one's abilities, body, or mind. It is easier to keep hair clean and healthy when it is short. Especially older people often have damaged and thinning hair and keeping a good, clean appearance is often emphasized in the SGGS. I have long, thick, curly hair and thus have to set aside an hour every time I want to wash it and comb it. If I chose to cut it for the purposes of making being hygenic easier, I believe that would be in accordance with the SGGS.
The real reason then for keeping long hair is in the history of the symbol. It is a matter of proclaiming one's religion to wear long hair and there is the question of whether or not you are flagging in your love for your religion if you do not keep long hair.
Personally, I do not believe that it is necessary to keep long hair to show pride in your religion. Some people do not proclaim their religion in this way. There are many ways to show your pride in your religion. Also, these days, many people would not know a Sikh, even if they saw him/her keeping long hair, so how does keeping long hair still serve as a badge of pride to those who are not Sikh. In addition, if you are not steady enough in your belief in Sikhism to die for it, then the symbol of kesh holds a meaning you are not ready to embrace and perhaps you should find that meaning in your heart before wearing that symbol. One common theme in the SGGS, starting even in the Japji Sahib is that the practice of rituals does nothing for the soul, that the meaning is within and not in ritual itself. Rituals may be discarded because they are not the heart of a religion and do not contain the meaning. They merely represent what cannot be seen. It is useless to keep long hair if it does not have meaning for you. And if you truly have pride in your religion and courage to stand for it, whether or not you keep long hair is a petty issue by comparison.
It may be becoming true once again that wearing a turban, keeping long hair, is a way of standing up for freedom of religion given recent world events. However, Sikhs are not being targeted for Sikhism, they are being targeted through ignorance. One could argue that keeping kesh is a way of dispelling this ignorance by showing that those who practice religions others may be unfamiliar with can be virtuous people, and are in fact people like everyone else. However, there is legitimate danger in some parts of the world in keeping long hair and the danger is from ignorant people looking to kill anyone who "looks Muslim" rather than from people who want to kill Sikhs. It is hardly dying in defense of the Sikh religion, or on a lesser scale, suffering abuse in defense of the Sikh religion, if your abusers don't recognize you as Sikh and aren't targeting you as a Sikh.
These are all things to consider in the idea of kesh and whether or not one should keep long hair.
Remember that belief in Sikhism, ultimately, is not something you wear. It is something that is on the inside and cannot be seen. The principles underlying instructions are the important thing to understand and to consider when making decisions about what is right and what is wrong.
I don't believe long hair makes a Sikh and I don't believe short hair undoes one.
