Vociferous means loud and insistent in stating an opinion. Not necessarily right — definitely audible.
It describes people, groups and protests, so a vociferous critic and vociferous opposition are both standard, and neither is a compliment or an insult by itself. The word is about volume and persistence rather than content. It is formal and appears mainly in writing. The Latin root means carrying a voice. Vocal does much the same job in one syllable and is far commoner in speech.
1adjectivevociferousExpressing opinions loudly and insistently.
“There was vociferous opposition from local residents.”
Latin
vōcifer
English, today
vociferous
From Latin vōcifer + -ous.
Etymology from Wiktionary, CC BY-SA