A lot of non Sikhs lead more Sikh lives than some Sikhs.
As for the others live and let live, we are here to serve. not to judge.
Are they right and are we wrong? If faith, even atheistic, makes them good people then they are in the right, we believe in tuning the inner to the Creator, to connect and to then emulate the qualities of Creator, to have no enemies, to be a support to anyone, to know the truth and live by it, to defend the weak, help the poor, most religions have aspects of these that can be respected and admired.
One does not need God, I personally see it more as the truth, plain and simple, it is a very basic view, but a God implies a bearded type on a cloud.
When you make a decision and you know its wrong, you cannot plead you did not know, because on a basic level you know what is right. A connection with this truth, this force of Creation, this ultimate eternal Ik On Kar, opens your eyes to bigger truths, it takes away the fog of life, it shows you how it really is.
To do this we read and understand the teachings of the ten humans that were blessed with enough wisdom and understanding to impart it to us, it is recorded in the volumes of the Sri Guru Granth Sahib Ji.