This is good stuff and I'm glad you're amplifying it. But like all good advice, it sometimes threatens to get misapplied. Yes, if you're evaluating an argument based on facts, you want to investigate the source. But if you're evaluating an argument based on logic, you only need to investigate the logic. Abraham Lincoln used to make this point a lot, usually with Euclid as an example: "If you tell me Euclid was well known as a liar, it won't make me doubt his proof that the angles of a triangle add up to 180 degrees".

In the last few years, I believe I've seen a massive increase in false factual claims (which is bad), a massive increase in warnings to be skeptical of factual claims, and in particular to check the sources (which is good) and a pretty substantial increase in people (absurdly) rejecting logical arguments because they don't know enough about the source (which is bad). I suspect the latter is a consequence of the many public warnings about checking your sources, and that it is perhaps the price we have to pay for those warnings. Of course it might well be a price worth paying.