I was just thinking about this yesterday.
I learned from ABC Warriors that a freedom fighter on one side is a terrorist on the other.
I learned from Zenith that God might not exist (believe me, this wasn't an idea bandied about much in 1980s Irish primary schools). I also learned from Nemesis that my school history books were talking pro-Vatican bullshit in trying to tell us that the Spanish Inquisition rarely tortured anyone.
I also learned from Nemesis that it was the cowboys, not the Indians, who introduced scalping (though someday Stephen Fry will tell me on Q.I. that this is a total myth, of course).
Finally, I learned from Sláine what the words 'eunuch', 'concubine' and 'impotent' meant.
Nice one, Pat and Grant! (I actually am grateful; 2000ad was a constant influence throughout my childhood and I wouldn't be me without it.)