Lyric discussion by perplexed_one 

Cover art for Mad The Swine lyrics by Queen

I would argue that Freddie meant to say that the Pharisees and most of the Jews thought Jesus as crazy, what with associating with thieves and whores. Second they thought Jesus to be arrogant because he was clever and humiliated the Pharisees in their own trap questions, and also because he proclaimed himself the son of God; hence they thought him to be swine, a pretty nasty insult considering pigs are taboo in Jewish culture. And the line "I guess I'm mad the swine" could be referencing Jesus' indifference to the pharisees insults.

also this song could be referring to Jesus exorcising the legions (of demons) from the crazy man living in the cave. he cast the legion into a herd of wild pigs, and they all ran in madness and drown themselves. cant remember what book and verse this is.

I personally dont think Freddie wrote this as an anti-Christian attack, just another perspective I suppose.