I almost let Juliet have the last word out of my enormous respect and affection for her

But that wouldn't be me

I absolutely understand what the RBST is doing and I support them wholeheartedly (and yes, with money too.) Whenever I am about to buy stock I do think about whether a rare breed would fit the bill, and whenever I buy rare breed I do consider whether it needs to be, or should be, registered.
If I wanted just one breed on a smallholding, and had no other pressures, then I expect I would have established a flock of registered Castlemilk Moorits and would no doubt be now embarked on a breeding programme to improve the fleece quality and consistency in my flock

.
Anyone in that position, I too would urge to
consider keeping a flock of registered rare breed sheep.
But I passionately believe that, where for whatever reason that is not the option taken, you can still be helping rare breeds in general and your chosen breed(s) in particular. Not least that your friends and neighbours will see these beautiful, usually hardy little sheep, and eat their wonderful meat, maybe spin their fleece, and all this awareness is very valuable.
I have a concern that if there is always so much pressure to make it only registered sheep, always to be breeding pure, then quite a few potential keepers may shy away from the rare breed altogether. And some keepers will take on the rare breed and try to do the registration thing - but not do it well, and end up registering substandard animals, registering animals with incorrect pedigree information, etc.
To me, it would be better to promote an atmosphere of support and encouragement
however people want to use the breed,
not pressurise people into only buying and breeding registered stock, but then actively encourage and support those who turn out to be good breeders to establish a registered flock. That way, the people who breed the registered stock are good at it : good breeders - good at picking tups for ewes, at knowing which ewe and tup lambs to register and which to leave unregistered; good at managing the pedigree information so that when stock is registered, the pedigree is correct; probably into showing to promote their own flock; etc, etc.
I absolutely do feel that I have had to withstand a lot of pressure to own and use an OSB sow, and Castlemilk Moorit and Manx Loahgtan ewes. In my situation, being a pedigree breeder myself doesn't float my boat and/or isn't an option, so my choices are to not breed at all or stick out my chin, thicken my skin, and buy purebred, whether registered or not, and breed them as I wish. Because the Saddleback x OSB pigs I've reared have been so spectacular both in terms of meat and of growth rates, and because Meg-pig is such a lovely friendly pig, a heck of a lot more people in my area now know about and might choose Oxford Sandy and Black pigs when their time comes. Equally, my crossing experiments with my unregistered but true to type sheep could lead eventually to a commercial use for one or more of these rare breeds being established - which surely would be in the interests of the breed.
And as to the scientific stuff about research only being valid when undertaken on registered stock... I completely understand the rationale, my degree is in Biology. However, having been a hill farmer for a few years now, and having seen a bit of some of the smaller scale breeding of rare breed pigs, sheep and ponies, I also know that, whilst a lot of pedigrees are accurate, they aren't all. Thankfully so, in some cases, as some of the hill sheep would've died away now but for a bit of judicious crossing on the quiet to reinvigorate the gene pool.
At the present time there is a lot of 'improvement' of certain native breeds of cattle going on. The schemes only pay the highest rate of subsidies for the use of registered pedigree animals, so the pedigree stock is being quietly infiltrated by usually undocumented injections of animals with a more commercial stamp - and sadly these are not always purebred, whatever the pedigree may say. The schemes which were meant to promote and safeguard the native breeds will end up eroding them substantially. It would have been far more helpful to give subsidies for the use of any native types, which would have left those interested in maintaining the true to type pure stock to get on with that, whilst still encouraging more farmers to consider that type of animal when stocking less favoured ground.
As with so much biological science, nature in the real world doesn't read the books or follow rules.

So my position is this. I applaud good breeders of rare breed stock who register and breed from only the best, true to type, correctly identified individuals.

To anyone considering taking on sheep, or pigs, or ponies, or cattle, or any livestock, I do encourage them to research the relevant rare breeds and to choose one if it suits their situation. If they know that breeding pedigree stock will interest them, and that they will be good at the traceability side of it, then of course I would urge that they establish a registered flock. However, if they do not want to go that route, either because it doesn't interest them or because they know they would not be good at maintaining the traceability and/or making the register/not register decisions, but they still like the look of the breed, then I would say that by all means they should consider buying animals of that breed and breeding them pure if they like, or crossing them if they prefer. So long as they don't deprive the pedigree breeding programme of good examples of registered animals by only buying top quality registered animals to then breed unregistered or crossbred offspring, I see no problem, quite the reverse, in these people buying registered or unregistered breeding stock and using them as they wish. I would prefer them to do that than to be pressured into trying to do the registered flock thing and doing it badly, or to be pressured into not using rare breed animals at all because they know they wouldn't be good at doing the registered flock thing and are made to feel that doing anything else with that breed is somehow harmful to the breed.
Just my opinion

- but passionately held.