The first counterargument you could advance is based on Socrates' assumption about the facts of the afterlife. He argues that either it is like a deep sleep and thus pleasant or that he will meet the famous dead and converse with them. He does not raise the possibility that he may go to an unpleasant afterlife.
The other possible counterargument is one that Plato puts in the mouth of Crito in the dialogue Crito, namely that Socrates' arguments are entirely selfish. Is Socrates shirking his duty to care for his wife and his children? By not arguing more strongly against his accusers (or perhaps accepting the help of the famous speech writer Lysias), did Socrates endanger his followers who had put there trust in him?