I don't agree with that for the simple fact that it's impossible to define in an incontrovertible way "virtue and honor" without resorting to some kind of spirituality. So yeah there can be honourable atheists, that's just because they accept to live like if they were religious without any real reason.

I think it is inborn for some people. To put it another way, it is possible for someone to reject religion "ideologically", but still conceive of his self and his personality in an integral way that encompasses not only the material self, but also the spiritual self and higher principles. Honour and virtue are valued not because of this or that reason, but because of a given nature and an affinity for those things. The danger in these cases is the possibility of eventually adopting ideological materialism and being affected by that outlook in the long term.