I am sorry to read your post above, a few points for your perusal brother
1. You are confusing family pride with Sikhism, they are two different matters, what is happening here is nothing to do with Sikhism, but more to do with the way your parents wish you to behave. I am sure even atheist parents have the same problem keeping their kids off drink and soft drugs, dating etc. You should not take this is a divine judgement and it should not interfere with the relationship you have with Creator.
2. You are angry and depressed because as human beings we wish to be accepted for who we are, not who we wish we were.You want your mom to accept you regardless what you do, or what you look like. She on the other hand, having spent the last 20 years raising you, and feeding, clothing you, feels a certain sense that you are about to do something terribly wrong and will say or do almost anything to stop you doing this, I am sure she has shed a few tears too, possibly a few more than you, as she may unable to confide in her husband, your father, for fear of making things worse. I think you are being slightly selfish here in not understanding how painful it is for Sikh parents to watch their kids lose their physical identity.Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/sikh-youth/38179-considering-cutting-my-hair.html
3. Your post is bitter and angry, if you are not careful, you are going to lose your family, albeit in the short term, and you are about to bring a lot of sadness into several lives, what your mom is saying, not in the most diplomatic fashion, is that while you live under the umbrella of the family, credit cards etc, you should respect the way of the family. Sometimes we do things for reasons we are completely unaware of, sometimes we want things for reasons we do not know, I sense a rebellious streak in you, the desire to be your own person, not a clone of the family, is it this streak driving you to show the rest of the world you can be your own person? but at what cost?
Let me give you an analogy, a family had a successful business, and had one son, the father had put everything in this business, and it had grown into a well oiled money making machine, business was done with honour, truth, happy customers, happy suppliers, as the father grew old, he wished his only son to take it over, but the son wanted to be an airline pilot, it was always understood that the son would take over, but one day the son revealed he wished to leave the home and become a pilot. This family would suffer in exactly the same way as yours, it has nothing to do with religion or God. It has everything to do with tact, diplomacy, understanding, compassion, gratitude and TIMING. Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=38179
No one is saying do not live your own life, but the way you are dealing with this problem is as a child, you want something, and you are willing to put these needs and wants above everyone elses, no matter what the consequences.
My advice? You wish to do something, your parents wish you not. Welcome to life in millions of Sikh, Hindu, Christian and Atheist households, deal with the problem with love, truth, understanding and compassion, if I were you, I would set a date, say age 22, and if by that time, you are still feeling as you are, you should be allowed to do what you want, this means that firstly those around you are aware of how you feel, and secondly, you all have time to get used to it, and maybe your parents will use the time to gently let family know, so that it is not a huge shock to all and sundry.
You will then be able to achieve what you wish with some dignity, and by causing the least amount of heartache,