Free speech is there exactly to protect minority opinions because sometimes it happens people in minority are right.
Every major movement started as minority, by definition. Free speech protection is there to make sure we can have smart people notice a problem and then express their concern and be allowed to voice it so that if they can gather enough movement to make a change there can be a good change.
It is sad that this can sometimes lead to aberrations like anti-vac movement but it would be a horrible idea to argue this is a reason to throw free speech protection out. Instead we should demand lawmakers to grow a spine and recognize there is no basis for anti-vac movement and enough is enough. Sadly, vote counting is much more important nowadays than sound medical advice.