Stating the following is an opinon:
" I personally think that most people I have met are using ADD as an excuse to get drugs "
Which is fine. Noone can argue that.
Stating the following in NOT an opinion:
" Most people who say they have ADD are only using it as an excuse"
Which is not fine because you are stating is as you would a fact of which I could find 1000000 reputable sources that can scientifically prove you are wrong. Which makes your opinion, not an opinion. It makes you WRONG.