Thinkers often tried to justify their failing (or things perceived as ones in their time) by bullshitting.
Some try to pass it as religious revelation, some build entire philosophy on premise "I can't be bad, therefore it's good", and so on.
Historical context: Greek society was overly masculine, man was always expected to be a top, an active predator and penetrator. Main course of male-male relationship was a pederasty, while equal relationships were considered "sissy stuff".
And in Plato's period all homosexuality was dubbed shameful, so he was trying to exonerate himself.
