Possible Clues:

• ''I agree''
• 'Same'
• Social justice hashtag
• Time's Up movement kin
• 'I feel the same way!'
• Hashtag that took off in 2017
• Movement spearheaded by Time’s 2017 People of the Year “Silence Breakers”
• Movement started on social media in 2006
• “Ditto!” (and a hint to what’s in the grid-spanning answers)
• Joiner's cry?