The Pope is wrong. While he might find it bad form to speak poorly of others the Lord Almighty (who outranks Francis) commands that we are not to bear false witness.
Therefore you speak the TRUTH be it good or bad.
Pope is not wrong. You may be misinterpreting to whom he's speaking and taking his message out of context. For example, he could be speaking about the media who has lied, twisted stories to defame someone just so they could keep their jobs ($$) and be the focus of attention. The media would be Judas. Those who repeat the media's lies, would be little judasses because they are magnifying lies and sacrificing someone good so they could make themselves look good and knowledgeable. They would be gossiping. THEY would be the ones bearing false witness!!
Now, if you say the media is lying and have facts to backup your position, you are then defending the truth and the person who is being defamed. You are not bearing false witness but are setting the truth free! Just make sure that while defending a good person, you do not put down the bearer of lies. Might as well not mention the liars/gossipers because that would still keep them on a pedestal.
That's what I get from Pope Francis' message.
The Church teaches against the sin of CALUMNY, which is speaking what might be the truth about someone, but doing so only to try to tear down that person, PERSONALLY, in the eyes of someone else, in order to hurt them. This isn't the same as pointing out what we might consider an error in someone's political views, in order to advance our own.