No doubt Guru Ji met the " worsest of the worse" and blessed them with the greatest gift of life . But by no means are we Guru Ji; however, at the same time we are not Yogis who try to avoid people who are lost.
I believe who ever I meet in life is arranged by Guru Ji If I happen to come across an athiest I wont run away or treat them as they dont exist. As long as we are japping naam then nothing will bring us down. if we are not japping naam then we are no differnent then the athiest. This does not mean we should try to go out on a mission and try to convert all the Athiest into Sikhi. Sikhi comes at a heavey price its not meant for everyone especially athiest who have no interest in God. I remember last year a relative who was an Athiest was staying with us. He was going through a hard time in his life. He eventually started reciting paath and thinking more about God. He even asked me if he prays to God will his situation change. I said yes if you do so with faith. He must of prayed because he got out of the struggle he was going through. By no means is he a Gurmukh or a Gursikh in fact he has somewhat gone back to his old ways because of the environment he now lives in. Anybody can change if they are spoken to with the Love of God, but if someone is fully determined to never believe in God then such people are simply cursed.
The phrase in Ardas "Nanak Naam Chardhee Kala tere bhanee sarbat ka bhala" does not exist in Gurbani. The phrase simply encourages us to hope for the best for everyone including athiest. We are not suppose to bare animosity towards anyone just because they dont share the same beliefs as us. This doest mean we freely socialize people who have no interest in God. Guru Ji says even the pig is more valuable then the athiest since the pig eats up all the garabage of the city while the Athiest is simply useless.
ਕਬੀਰ ਸਾਕਤ ਤੇ ਸੂਕਰ ਭਲਾ ਰਾਖੈ ਆਛਾ ਗਾਉ ॥
There is no value in freely socialzing with non-believers. The only value is socializing with devotees of God even if its just for a couple of seconds.
ਕਬੀਰ ਏਕ ਘੜੀ ਆਧੀ ਘਰੀ ਆਧੀ ਹੂੰ ਤੇ ਆਧ ॥ ਭਗਤਨ ਸੇਤੀ ਗੋਸਟੇ ਜੋ ਕੀਨੇ ਸੋ ਲਾਭ ॥੨੩੨॥
Our life in this world is extremely short. Whatever free time we have should be spent amongst the faifthful. At work and school we come across Atheist this doesnt mean we shun them. Socialzing and communicating ( interacting) are two different things. Only if we socialize ( eat from , hang out with , etc) with Athiest does it have an effect on our jeevan.
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥
With SatGuru Ji's Kirpaa, I started to have faith in Baani, in His Sikhi, in His Naam. Guru Sahib also blessed me with Sarbloh Bibek, come to think of it, this all happened in a couple of months! So yes, Sangat does affect you, as stated by Bhai Narinder Singh ji.