Health, who says that most poskim hold like Rav Moshe. In any case, halacha k’rabbim is only when there is a discussion and vote, as in a din Torah or on the Sanhedrin. Just out of curiosiy, do you wear a tallit katan?
Simcha, my understanding is that you get points for doing it but do not lose points for not doing it. Sort of like an extra credit question on an exam.