This is an interesting discussion. The SSiW method has so far worked so well for me that I don’t feel a need to use Memrise to learn the vocab. By the time I’ve done a lesson or two with the repetition, I feel like I know the words. (I hope this doesn’t sound snobby - it’s just my experience thus far.) However, I am using Memrise to learn additional vocabulary outside of SSiW.
I totally agree with this. Aran has put a ton of time and effort into making a fantastic learning method, and should retain all the rights to his material, and the income that goes with it.
I get the impression that Aran is passionate about promoting the Welsh language, and I am very grateful for that, and for his generosity in making the entire first course and first level available for free. But that doesn’t mean he is giving away everything he’s done - this is his business, and he has clearly put (and continues to put) a huge amount of time and thought into what works, what doesn’t, and how he wants to do things. He deserves to be able to make an income from his labor, and grow his business in whatever way he chooses, without people appropriating his work.
The trouble with the internet age is that many people think that they can just take whatever they want because it’s out there and it “should be” free. The same people probably wouldn’t shoplift physical property. Intellectual property is owned by the creator just like physical property is owned by the purchaser. On the other hand, I think many people (like the original poster) are nice, and just want to share, and they simply haven’t thought about what they are really doing. I understand the sentiment that “I’ve done all this work to make this Memrise course, I’d be happy to share it with others” - but doing so without having asked permission is wrong, in my opinion.
I don’t think there is anything wrong with someone making an SSiW Memrise course for their own personal use. It just needs to stay private, so it’s not available to anyone else.
Regarding the SSiW philosophy on not reading/writing until later:
The thing that people living or who have lived in Wales have, that some of us do not, is prior exposure to the language, especially to how it sounds. Even if you only spoke English to start, you already have the right vowel sounds and the right accent. So the fact that you have seen Welsh written on a daily basis is not as critical, in my opinion. For those of us outside of Wales, I think it is really important to avoid the written language in the beginning. We need to be solid on the speaking, on the sounds and cadence of the language, on the accent, before we start looking at reading/writing. Maybe if I were learning a language with a totally different alphabet, it might not be as important, but Welsh has letters that look like English letters that don’t sound at all like their English equivalent. And the vowel sounds are very different. I remember hearing words like “mewn” and thinking how different they sounded, and that I’d never figure out how to say them properly. But it is getting easier with time and experience (although my American accent will never go away 
).
Unfortunately, @aran, I don’t think I have any good answers for you. Since pretty much anyone can contribute to Memrise, I don’t see how you can stop them from using your logo or materials, or make them put some kind of disclaimer. It sounds like your experience with YouTube was awful but in the end I think maybe you need to contact Memrise and ask to have courses that infringe on SSiW removed. We can only hope it wouldn’t be a terrible battle to do so.
(Okay, I’ll stop, I think I got a bit passionate there myself Hope I haven’t offended anyone - that was not my intention at all. We are each just giving our own opinions.)