Apparently that 'unnecessary permission check' was necessary. ¯\_(ツ)_/¯

app/controllers/messages_controller.rb

@@ -1,5 +1,7 @@
 class MessagesController < ApplicationController
 
+  before_filter :check_permission, only: :destroy
+
   def index
     if current_user
       @messages = Message.where(user_target: current_user).page(params[:page])
@@ -70,4 +72,14 @@ class MessagesController < ApplicationController
 
     params.require(:message).permit([:text, :user_target_id, :user_sender_id])
   end
+
+  private
+
+  def check_permission
+    @message = Message.find(params[:id])
+    unless @message.user_target == current_user
+      flash[:alert] = "You are not allowed to view this message"
+      redirect_to home_statics_path
+    end
+  end
 end