I think there are certain potential misconceptions about philosophy and StackExchange involved here which I would like to address, namely:
Philosophy as fact
The sense in which sources are factual bases of answers
Philosophy.SE as being about philosophy vs. being for doing philosophy
Factuality, philosophy, and StackExchange
[W]hy do we assume that these references are concrete enough to act as the basis of "fact" towards supporting an argument or viewpoint?
According to modern understanding, that which states/ensures/produces "facts" is science. There are some authors who want to establish philosophy as science or "science of sciences", but usually, branches of philosophy that "mature" into science proper are seen as just that - a new science - and in a sense exactly not philosophy anymore.
Philosophy is about arguments and reasons, about meanings and the "why"'s and "how"'s that are not answered by facts. In other words: That which stands into question - in a sense the opposite of that which is "factual", i.e. that which just is (obviously, insofar that which is stands into question, it is a subject of philosophy). Philosophy obviously has to include "facts", but facts are - at least according to the vast majority of philosophers - about the world and play a role of justification in philosophy.
Now, StackExchange, by its very nature, bids us to build our answers on facts. So why use texts of philosophers of old (or not that old) as the basis of answers here? Why use references instead of allowing for ingenious, revolutionary, progressive thought? Because references constitute a factual basis, in a sense: They, as a matter of fact, state what they do state, are publicly available and in this sense objective, similar to the insights of science. The difference is that the intension (mind the "s"!, technical term!), i.e. the referent and guarantor of the objectivity, is itself not a fact in the world, but rather a meaning, i.e. the sense of that which has been written.
To refer back to the "factuality" of philosophical sources: So yes, obviously the content of the answers is not certain, even if they are well-sourced in philosophical references, because philosophical propositions are philosophical insofar they have questionable truth-value. But it is certain that these are (the) answers that exist.
The problem of knowledge about philosophy vs. doing philosophy
One of our best-voted Meta-questions is Friends, we are not philosophers and the only, clarifying answer correctly states:
Just to clarify [...], the point is not that none of us are philosophers (which would be false), it is that we are not here in our capacity as philosophers, but in our capacity as subject matter experts about the field of philosophy. Our task is to answer questions about philosophy, not philosophy questions per se. The reason is that StackExchange itself is oriented towards questions with well-defined, objective answers, and few (if any) open philosophical questions have those.
A similar point has been made (based on the help center guidelines) here in an answer of mine regarding "philosophical questions".
Long story short: Since StackExchange demands that questions are answerable (and answered) based on facts rather than opinions or standpoints, we have to base answers on the factual basis there is in philosophy: formerly written texts. Original philosophy is obviously important for the subject matter of philosophy itself, but Philosophy.SE is not a place where it does fit.
Similarly, an answer based on a revolutionary, yet undocumented (and untested) theory on Physics.SE would not be received well. In a sense, StackExchange is conservative, since it is supposed to build a databank of and thus preserve existing expert knowledge about solutions within the various subjects in form of a Q & A format. It is not supposed to be the platform for the promotion of new, unprecedented and therefore "experimental" content that - even if based on and originated from expert knowledge - itself is not part of that which we commonly call "knowledge", but perhaps rather "intuitions" or "hypotheses".
Conclusion: Even if all philosophical writing could be rendered as "mere, unertain hypotheses" (taking an extreme limiting case), it could still be the basis of an answer on StackExchange since that these hypotheses exist and how they are argued for is still factual. To the contrary, mere hypotheses (even if they may turn out to be revolutionary and "correct" or "accepted") do not meet this minimum standard of StackExchange.
((Disclaimer: I am aware of the fact that about 80% (conservatively estimated) of the questions and answers do not meet the standards described here and in the help center. This is unfortunate, since it repels experts from participating and berefts the site of valuable contributors, see e.g. here. It will take a huge joint effort of a significant part of the community to change that, as there is no way the moderators alone can do it. Opening meta-threads with proposals for and discussions of a definite policy as well as voicing positions on meta in general is explicitly welcomed!))