The correct answer to this open question is the following.
Although there are no options attached we can say the following.
What does Fortas mean when he states "if we are not to . . . Teach youth to discount important principles of our government as mere platitudes"?
What judge Fortas meant was that American youngsters that are limited in their rights as students would be disappointed and are going to find it very hard to truly believe in the idea that the government has a true interest in them. Students would doubt the merits of the government.
We are talking about Abe Fortas (1910-1982), who considered that students could use armbands and that did not interfere with other youngsters because these bands did not threaten other students neither represent a risk. He thought that students just were exerting their right to express their opinion,