I hate those words.
When someone prefaces a statement with those words, they are insulting your intelligence. They are saying to you that no matter what you think, what they are saying cannot be denied as truth. They are trying to force feed something into your brain, and telling you to accept it without questioning it. They are promoting themselves, or their cause, as the indisputable altar of truth.
While many folks use this preface to their comments, it is especially heinous when someone in politics spews it out. People in both parties are guilty of it, but I find a preponderance of violators using it are on the left. If you listen to left wing pundits, I guarantee that at least 50% of them start their spew with that preface.
When someone spits this out to you, whether it is in person or through the media, you are about to be bombarded with either 1) their OPINION, or 2) an out and out LIE. Your internal bullshit detector should immediately go off, telling you to either disregard whatever this person is saying, or carefully examine it to determine for yourself how much credence to give it. No matter what else you do, do not accept what they are saying as the 'The fact of the matter is' ...