And, as I start this, that goes for me too. I am decidedly opinionated and there's no reason for anyone to necessarily believe me if I don't have, say, video or audio or a link to a document to back up what I say. I've noticed lately a rash of assertions about various political issues that merely put forth a premise but without anything at all to back up those assertions. When that happens, I like to think that people will be energized enough to push back and say "Give me examples" or "Why are you saying that, what proof do you have", rather than just believing what very likely is bullchit. 

This is a logical reasoning fallacy entitled Proof by assertion or otherwise known as rhetoric

Argument by assertion is the logical fallacy where someone tries to argue a point by merely asserting that it is 1, regardless of contradiction. While this may seem stupid, it's actually an easy trap to fall into and is quite common.

Rhetoric

It is also well known as rhetoric, because an assertion itself isn't really a proof of anything, or even a real argument - assertion only demonstrates that the person making the statement believes in it. An inability to provide anything other than an argument by assertion may be the result of brainwashing, basing ones belief on blind faith or ignorance as to what forms a proper argument. Those who argue by assertion often do think that they're making a real argument. They might simply not realise where they haven't provided a full argument. The point of constructive debate or discourse is to draw attention to this sort of thing, and for people to further develop and evolve their arguments in response. A truly fallacious argument by assertion is when someone continues to assert without advancing their argument, even after it has been pointed out.

A repeated argument by assertion can also take the form of non sequitur that requires little effort to make and is therefore often used to fatigue people who make actual arguments - sometimes combined with the infamous Gish Gallop. They will then bow out of the debate, usually exhausted, having lost faith in humanity and muttering "how the hell do you reason with these people?!?!" through grinding teeth - at which point the individual making the assertive argument simply declares victory.