Are people inherently good according to Plato?
This may be a delicate question. On the one hand, Plato's Socrates asserts, in the Phaedo, concerning the misanthropist (hater of people), that only few people are genuinely good or evil.
Is it not obvious that such an one having to deal with other men, was clearly without any experience of human nature; for experience would have taught him the true state of the case, that few are the good and few the evil, and that the great majority are in the interval between them.
On the other hand, Socrates asserts in the Protagoras, that no person does evil except out of ignorance. So that no person is inherently evil:
Then, I said, no man voluntarily pursues evil, or that which he thinks to be evil. To prefer evil to good is not in human nature; and when a man is compelled to choose one of two evils, no one will choose the greater when he may have the less.
Concerning the Gods, they have been doing a lot of mischief in the Greek mythology. Socrates and Plato, however, considered this preposterous. The Gods, by them, had to be virtuous. In the Republic, Plato's programme for an ideal state includes related censorship of Homer and other poets over this issue.
Then we must not listen to Homer, or to any other poet ... And if any one asserts that the violation of oaths and treaties ... was brought about by Athene and Zeus, or that the strife and contention of the gods was instigated by Themis and Zeus, he shall not have our approval ... he must say that God did what was just and right.