Justice and mercy are not in conflict in healthy relationships; they complement each other because they bring the necessary balance that helps friends mature into a complete Christlikeness.
The downside is that some people lean too heavily into mercy, excluding the essential corrective care, warning, or justice that friends provide for friends.
Of course, the heavy-handed, mean-spirited, authoritative types speak of justice, but it's perverted.
When you can pneumatically care for others by applying mercy and justice appropriately and practically, you're a good friend.