Actually Kirk says "we have no need for gods." Knowing Rodenberry's secular humanism, I wouldn't be one bit surprised that the next sentence ("We find the One quite sufficient") was forced on the show by advertisers against his will because they didn't want to antagonize people. This is my theory, anyway, since the two statements are mutually exclusive.
He says both lines in that episode.
Not necessarily. In the context of Greek "gods" (normally written with a small "g".) Kirk seems to be drawing a distinction between the Greek Pantheon and Monotheism as represented by Judaism and Christianity. (Although Christianity is a little more confusing on the point.)
Gene Rodenberry may have believed in secular humanism, but I think he was sufficiently aware of sentiments in the rest of the nation so as not to deliberately antagonize the dominant belief system. Had he left it at "We have no need for gods", people wouldn't hear the small "g" implying "Greek gods". They would assume he had deliberately insulted the vast bulk of his audience.
Rodenberry wasn't stupid enough to believe that wouldn't come back and bite him in the @$$. The only way to make this point without blowback was to add "We find the One quite sufficient", so that the people listening would understand that he was referring specifically to the pantheon of Greek "gods".
Even if Rodenberry was stupid enough to try that, I'm pretty sure everyone else on the set would have counseled him properly about what a mistake that would be.