How could one justify the accusations against Socrates in Plato's Apology?
Plato's portrait of Socrates is extremely persuasive to contemporary readers. It is worth noting, however, that not all audiences were convinced either by the historical Socrates or by the Platonic ones. The ancient Athenians did condemn Socrates to death, and many 18th and early 19th century writers tend to view the case for Socrates in Apology as one in which the arguments on both sides were compelling.
It is, therefore, worth asking if there were any merits in the accusations against Socrates. First, on the question of introducing strange deities, Socrates evades the question by saying that he does participate in the state religion. This begs the questions, as does his account of the limitations of his daimon. He does, in fact, seem to have innovative religious ideas, follow a deity not part of the established religion, and incite others to scepticism about accepted religious practices (e.g. the Socrates of Euthyphro could be accused of fomenting religious doubt)
For corrupting the youth, there again is some question as to whether, as many eighteenth and early nineteenth century critics point out, he tended to undermine established belief structures, and put nothing in their place, leading intelligent youth to conclude that all values being uncertain, one might as well act out of pure self-interest. As J. S. Mill points out, Socrates has no effective answer to Callicles.