Am I wrong for thinking that my friend's high school plan is dumb?
Why do you think your plan is dumb?
Because even though they are good students, there are other schools that are much more better
The way that you can tell your friend that you disagree with them without hurting their feelings is by politely stating your opinion. You can let them know why you disagree.
I'm just going to go along with what my friend wants to do, it's not a big deal.
It's great that you want to respect your friend's choices about their life. This will ensure that you are supportive to them.