To Enable ARD for all users type in Terminal:
sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -configure -allowAccessFor -allUsers -privs -all

This will change the access from All users to only specified Users. *Note you have to specify the users from a different command.
/System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -configure -allowAccessFor -specifiedUsers
Add all privileges to the User "User1"
/System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -configure -access -on -privs -all -users "user1"

Disable ARD
/System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/kickstart -deactivate
