vocal critics

• outspokenFreely expressing opinions
• detractorsPeople who criticize
• dissentersOpponents of prevailing views
• opponentsThose who compete against
• naysayersThose who dismiss ideas

skeptics · protesters · whistleblowers · pundits · commentators · harsh · condemn · denounce · attack · blast · slam · rebuke · outcry · backlash · pushback · scathing · fierce · relentless