I'm not going to discuss the Somerton response video in detail, but I wanted to make one quick point. About his explanation that his failure to cite derives from memory issues. Let's take that explanation at face value for a moment.
Memory issues (either of the diagnosable or undiagnosable variety) are very common in academia. I have a pretty terrible memory myself, also exacerbated by a serious head injury. And even a moment's reflection will reveal that academia is also chock full of old people. A poor memory in academia is not a novel thing at all.
So, how do you cite responsibly if your memory isn't perfect?
You don't rely on your memory to cite.
Even if you have a pretty good memory all things considered, trying to cite from memory is a suckers' game and it will betray you someday. You'll get two dates mixed up and then your argument is nonsense. You'll forget where you heard something and assume you came up with it. You'll miss some crucial detail when trying to reconstruct a claim you read three weeks ago and accidentally say the opposite. Your memory is not a good tool for this purpose.
So use a better tool. Take notes as you're reading. Whenever you're looking at something pertinent to your next project, you'd better be a) writing down what the source is and where to find it and b) what the key point you've found in it is.
Thankfully, we live in the 21st century and this is now a very easy thing to do. There are programs that will do most of the tedious author-date work for you and automatically pop up a little spot to write down your key points (I use Zotero, but there are other citation managers of similar quality out there). Then, before it's time to write, you can sit down, look at a convenient list of everything you've read with the key points all ready for you, and be very sure that you're not making any mistakes or plagiarizing anyone. The other bonus of using a citation manager program is that when it's time to construct the biliography, you just press a button and it's all there. I can't recommend these programs enough to anyone who is doing academic work of any kind.
There's an ask that's been sitting in my inbox that prompts me to talk about the 'lay academia' of sites like tumblr and youtube. I've been thinking about it for a while, and I will eventually write a big long piece on it, but the short version is that I think that lay academia is great. I love that tumblr is basically a collection hub for the research interests of thousands of scholars, and that there are more people who want to be scholars than I could possibly have imagined. My good dead friend Aristotle once said that 'all men* by nature desire to know' and buddy, you bet they do. And I also see a lot of these lay academics rediscovering the citation techniques of the real academe, which is great.
But when you've got a lay academia that hasn't been trained in the methods that professionals use, that lay academia can produce misinformation and model bad scholarly habits. Somerton is showing us that right now. If what he's saying about his memory is true and exculpatory (which we are assuming right now) then he should never have been trying to write public essays by memory. That's undergrad behaviour. That's a mistake you make when you haven't learned better the hard way yet. It's a clear sign that he was never prepared to do scholarly work on a public stage. It's cool that these websites have democratized the academy, but the consequence is that you can get very big without being very good. Or even knowing how to be good.
So, if you're reading this and thinking 'oh, but my memory-' well, this is your sign. If you have a tool you know doesn't work that well don't keep trying to use it. Find a strategy that will let you do good work without relying on that tool. You can't learn anything from Somerton. So at least try to learn from his mistakes.