I am going to argue that a citation or link needs to be mandatory for every question, otherwise the question should be closed. I recognise that this a perennial question and proposition that has been raised numerous times.
The standard of question crafting seems to be quite low and it takes a disproportionate amount of time for commentators to support and develop the question. Many questioners are first timers, with very few providing ongoing engagement or interested in answering questions. Closing questions off without links or citations will encourage deeper and more thoughtful engagement.
Many questions are not really related to research or subject to any serious consideration. The questions that get me upset are interesting questions but are based on opinion, TV shows or a general feeling without any attempt to read or google any background information. As the result the question is very conceptual, and the OP has not done the required reading to understand the complexity of the background answer nor the research basis for their opinion.
I have had responses where the OP gets frustrated that their broad comfortable generalisation is fictional and not based on research, resulting in discouragement for people who answer.
When prompted for a citation or link, negative or sarcastic remarks tends to be more likely than not. OPs can feel that responders are being too "intellectual" and "too academic" or inaccessible which has been the previous worries in other posts. However, there are Reddit, Facebook and other groups that do not require any standard that they should be posing their questions.
If we make closing questions without links or effort the norm, we can protect those who are interested in developing an engaged and stimulating SE without subjecting them to hostile OPs. The baseline effort for a question should at least be a simple google and ideally a nice journal citation. There are plenty of open-access journals accessible through google as well. Hopefully taking these steps will increase the standard and the quality of questions resulting in more interest and engagement. Thoughts?