Dishonouring one’s hair is one of the four cardinal sins, which the Guru has told a Sikh never to commit. A Sikh doesn’t disfigure their hair from head to toe because Guru jee told us to keep sanctity of Kesh (hair). Nothing else matters. A Sikh does what their Guru told them to do.
mweI siq siq siq hir siq siq siq swDw ]
bcnu gurU jo pUrY kihE mY CIik gWTrI bwDw ]1] rhwau ]
“O mother, True, True True is the Lord, and True, True, True is the Guru.
The Word, which the Perfect Guru has spoken, I have tied to my robe. ||1||Pause||”
(Ang 1204)
A Sikh lives in harmony with God's Divine Will and blessings. God has given us the gift of the human body. The hair is special due to the fact that Naam abides within each and every pore of hair on the body. So when we Naam Jap (meditate on the Lord) the hair is a spiritual tool, which vibrates and absorbs Naam.
rom rom mih bsih murwir ]
“On each and every hair, the Lord abides.”
(Ang 344)
gurmuiK roim roim hir iDAwvY ]
“The Gurmukh meditates on the Lord with every hair of his body.”
(Ang 941)
Bhai Desa Singh, records in a Rehitnaama the words of Guru Gobind Singh jee:
qn ies ky isr kys ju dIno[ so ieh qn iSMgwrih kIno[
dwVHw mu`C isr kys bnweI[ hY ieh idRV ijh pRBU rzweI[
myt rzwie ju sIs muMfwvY[ khu qy jg kYsy hir pwvY[
”God created the whole universe and then he fashioned the human body. He gave men beard, moustaches and hair on the head. He who submits to His Will steadfastly adheres to them. They who deny His Will how will they find God in this world?”
In addition, hair and nails are totally different. Having long nails inhibits use of the hand and is dirty with filth being stuck under the nails as well as bacteria. Long hair is quite healthy as it is even a reflection of good health: (when healthy, hair shines, when sick, it loses lustre), it is also not an impediment to daily life. In fact, you'll be healthier if you have long hair: body resources go to replacing the hair that was cut: isn't it a slap on the face when you shave and then a day later, the hair returns? Nails, if left uncut, will break; hair never will.