That's not what Trende's saying.
His point is that you can say nothing.
You can say: "I believe that your religion is wrong and mine is right."
Or you can make a conscious choice to say: "You are a demon-worshipping affront to God," & then act surprised that it offended people
Why are people continually shocked at the existence of sincere religious differences? Jews think Jesus was a liar, Christians think Ganesh is a demon, Scientologists think all other religions are evil tricks by alien ghosts or whatever. Not all religions are universalist John Lennon slop. Sometimes people really mean it, which necessarily means thinking people of other religions (or none) are deeply, profoundly wrong about the most important issue in existence. Saying this should be unacceptable is tantamount to saying religious sincerity should be unacceptable.