Quality of citations
Weight and quality of assertions and claims should match weight and quality of quotes and citations
Not everything that might benefit from backup from other sources needs to be an academic history research paper.
Illustrating a peripheral point in an answer can give you a hard time finding academic or otherwise reliable online sources. Contrasting supposedly common knowledge or basic facts with historical research can give you a hard time backing it up with online articles or comparable sources alone. Sometimes such a scholarly source exists, but it is either behind paywalls or it is simply not online at all.
The point is, anyone striving to provide an answer is regarded as someone having a say because she knows something. Something more than the asker, something more or in addition or improving on, correcting previous answers. Furthering the discussion.
Mere statements are not very helpful in these cases. Arguments need some kind of backup most of the time. Pointing out a logical flaw in a line of reasoning might be sufficiently called out by explaining why you think it is flawed. But when discussing the pros and cons of conflicting sources or narratives you most often need to quote that, refer to that, give links to that. We need the transparency most. Everyone should form his own opinion and be able to check the sources that form the basis of your post.
As an answer poster you are also a judge, a gate-keeper an evaluator of the material available to you, of your own knowledge. As such it is up to you to find the best evidence, the strongest argument the best data to backup your claims, your arguments or reasoning. Low quality sources are permitted! Low quality sources are also miserable and shine a bad light on your answer and on you.
That is why we need reliable sources. If you want to backup your claim about perhaps well-known facts that are non-central to your argument, then higher standard historical sources might not be the easiest to accomplish what you want to say.
Peripheral sources I would like to call them should be fine to illustrate, to give context to weigh the arguments. Central claims need reliable sources central to the field of discussion. One might contrast yellow press articles with what books or research articles have to say about a certain topic. It will be almost fruitless to just refer to personal anecdotes or a TV host's statements to backup your statement.
You do not know or have the truth. Your sources do not have or know the truth. –– Everyone is entitled to his own stupidity. Or geniality. There is always room for improvement.