So anyway on the subject of what Baha'i think of atheists we should also look at what Baha'u'llah thought of atheists.
Although I don't know of any specific references to atheists by Baha'u'llah (he polemicises what he terms "the ungodly" however he appears to have meant people deprived of virtue by this unfortunate choice of words) nonetheless atheists are a subset of non-Bahai, so the question remains are we to blindly believe the claims by Baha'u'llah of how Baha'u'llah regards non-Baha'i, or should we as critical thinkers evaluate his actions for divergence from his words?
If we are to go with actions here is an interesting teaching of Baha'u'llah which seems to highlight what he truly thought of non-Baha'i in my view;
It is Baha'i inheritance law.
Baha'u'llah states, "Any heir, from whichever category of inheritors, who is outside the Faith of God is accounted as non-existent and doth not inherit."
Source:
Bahá'í Reference Library - The Kitáb-i-Aqdas, Pages 105-141
So according to my understanding any non-Baha'i child would according to Baha'u'llah's recommendation be cut of from the family inheritance which Shoghi Effendi has clarified applies only in cases of intestacy (where a person dies without providing a will) as if that makes such bigotry ok.
Here is Shoghi Effendi on the matter;
'…Although in the “Questions & Answers” Baha’u’llah has specifically stated that non-Baha’is have no right to inherit from their Baha’i parents or relatives, yet this restriction applies only to such cases when a Baha’i dies without leaving a will and when, therefore, his property will have to be divided in accordance with the rules set forth in the Aqdas.'
Source:
Bahá'í Reference Library - Dawn of a New Day, Page 77