I came to know about 'Gurbakhsh Singh Kala Afgana' who is the author of controversial book 'Bipran ki Reet ton Sach da Marg'. He questioned the basic tenants of Sikhism, including the ceremony of Sikh baptism (Amrit). He also questioned some of the Sikh hymns (banees) recited during Sikh baptism and daily Nitnem. Some of his views we can see on this link.
http://en.wikipedia.org/wiki/Kala_Afgana
I found a video which shows his interview.
Comments are welcomed if anyone knows about his views and thoughts.