I'm thinking of giving a presentation at school which basically criticizes most people at the school
Are you sure you would want to do something as risky as that?
Yes, I think it's important for people to know the truth about others
You shouldn't give a presentation that criticizes everyone at the school. If you have complaints about the school, you should air them more privately rather than doing it publically.
I don't agree with that at all.
I just think that might start a huge fight in the school. I recommend you do a presentation on something else.