Socrates was convicted at the age of 71 for "[corrupting] the youth of Athens, sophistry (fraudulent teaching practices), and heresy"[331]. It's not very shocking that he was criticized for his teachings, since they violated every standard that was established in Greek philosophy at the time. Contrarian thinking has never been a socially-accepted practice and everything that is considered outside of the ordinary is a negative form of thinking. However, it's safe to say that Socrates could back up everything that he said to his following.
It's important to note exactly what Heresy is, however, especially since it is one of the lower circles of Hell (http://historylists.org/art/9-circles-of-hell-dantes-inferno.html). Merriam-Webster has two definitions of Heresy. The first is "adherence to a religious opinion contrary to church dogma". The second one being "dissent or deviation from a dominant theory, opinion, or practice" (https://www.merriam-webster.com/dictionary/heresy). Since Socrates violated the ways of thinking in Ancient Greece, by definition, he earned his seat in the sixth circle of Hell. However, one question that rises in my mind is, "Is disagreeing a sin?" Socrates chose to teach lessons based on what he believed, and since it was considered outlandish, he was scorn by many and executed. However, it would be impossible to have every human agree to one method of teaching.