Because they are afraid to stand up the the fascism of liberalism. Only liberals seek to stifle freedom of speech. Now, if he were to wear a t-shirt that said, "I support a woman's right to choose!" he would lauded as a hero.
“Free Speech” is currently a one-way ratchet to the left.
I’m sure it would be perfectly OK, or at least a “free speech” issue protected by the threat of lawsuit from the ACLU,
if someone wore a pro-abortion or anti-Christian message on their shirt,
like the footed fish with “Darwin” on it eating the Christian fish symbol.
That little piece of hatefilled garbage puts the LIE to the claim that teaching evolution isn’t intended to destroy religion.