Drug Ba11ad... I think there's a lot of stuff that you just need to let go of. While I'm just as much of a Pac fan--and in a few cases, more so--as the next forum member, my admiration for Pac doesn't exaggerate who he was as a person.
Pac was influential, but it's not like he changed the world. He was an intelligent, talented man who did a lot of good things, but it's not like he cleaned up the ghettos and put minorities on the same playing field as the upper-class white Americans. He had a lot of great ideas that definitely would've made life better for a lot of people, especially those in the lower income bracket, but none of those things materialized.
As far as the good things that Pac did for the community, there were a few (randomly giving money to beggers and visiting kids in hospitals) but not enough to make a strong argument. A lot of Pac's best ideas either never happened or started but didn't take off. Examples? His idea to have rappers sponsor Pop Warner football teams and Little League baseball teams composed of good students was just what a lot of cities needed, but they never happened. Blame it on Pac's untimely death if you want, but it's not something that required years to plan. And the whole thing about him "sitting across from all the candidates at the next election" was just wishful thinking.
And let's not forget about all of the bad stuff. Pac was a guy who talked about ending black-on-black violence, saying "win or lose/ red or blue/ we must all stay true," but he got shot over throwing the first punches at a Crip. If you were in California in 1996, you'd understand the power that Pac had. While nobody was really "riding" on the East Coast, A LOT of us were all on the "Fuck Bad Boy and whoever else" bandwagon solely because of Pac. And it's not because we didn't know any better or out of ignorance, Pac had that powerful of a voice, and while he realized the error in his ways later on (hence the One Nation album), none of us got to hear it or watch the drama blow over, and as soon as Pac died, a lot of us had it in our minds that it was still on. The sad thing is, I was almost expecting (but not hoping) that Biggie would get murdered in a matter of months, and he did.
So in the end, I agree that your sister's teacher was probably a bit narrow-minded about Pac, but at the same time, that individual is only responsible for getting across the school's curriculum, and I feel that the teacher had every right to question Pac, but not to that level of seriousness (considering it's just a jack-o-lantern). While I see your point about Elvis and Marilyn Monroe, they're at least historical figures, whereas Pac is just a charismatic, talented black man with perhaps the most influential voice ever in hip-hop--for now. Maybe one day that will change, and he will be a more important part of music history. But all I know, is that after all those years of public school and five years of college, I have only had one textbook that ever mentioned "Tupac Shakur" (not counting the ones from my Sociology of Hip Hop course). While others underrate Pac as an artist, that doesn't mean that every fan of his can overrate him and call him some sort of revolutionary who changed the world. Just think back to Chris Rock from his Bigger & Blacker DVD:
"People always make shit bigger than it really is. People saying 'Tupac Shakur was struck down by assassins' bullets.' 'Biggie Smalls was assassinated.' No they wasn't! Martin Luther King was assassinated. Malcolm X was assassinated. John F. Kennedy was assassinated. Them two niggas got shot. I love Tupac, I love Biggie, but school will be open on they birthday."