I do not think it is a hundred percent necessary to provide sources to be taken seriously because some of it comes down to strict opinion. As long as the person brings up some valid points (whether they have sources or not) and explain themselves in a well mannered way they should be valid enough.
The truth is that there is no absolute truth. Therefore we can't know everything, no matter how many articles and other references we cite. We can take what we know about the world and question it and draw logical deductions about it based on common knowledge which would be difficult to dispute (i.E. The earth is round, therefore there is something stopping me from falling off). I say this because I often notice points being criticized for "not being cited", but if the point is logical in and of itself, what is there to cite?