Disagreement, fine. Trying to shut people up? Not fine. If you disagree, have the guts to face them and say it. If you are confident about your opinions, there is no shame in speaking up and anyone should respect it. But if you are going to hide and bash, you're just proving you know what you are doing is wrong. Criticize opinions, that's your right. Don't criticize a person's right to have them. That will never be your right.