First of all one needs to know their Identity. I am a Sikh and I am aware of Sikhi. If someone is doing something I do not have to do the same. I am an individual with the capacity to think on my own what is right and what is wrong. Unfortunately many of us do not think this way. If we see someone doing something we do the same. Example: If you are standing in traffic and you see a person run a red light the reality is many more people stand on that light will do the same if there is no traffic coming. Sikhs should always remember who they are and what Sikhi teaches us.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/sikh-youth/29160-keeping-my-bodily-kesh-hair-getting.html
If someone does something wrong because they are not aware that it is wrong, that is another thing. But if you know cutting any body hair is wrong and you still do it then what you are doing is wrong. If one calls themselves a Sikh then its his/her responsibility to follow Sikhi completely.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=29160

Waheguru Jee Ka Khalsa Waheguru Jee Ki Fateh