I castrate all my boys just cos they tend to trash the fences otherwise as I keep them until their second year. Have never had any issues of it seeming to cause them real pain/issues. I do them at 1 day old, (the ewes lamb outside and then are brought in for lambs to get dry and make sure they are mothered up and drinking, and then once castrated next day they go out again).
Only had one or two where I couldnt be happy that the balls were both present and correct and 'safely gathered in'; these were left uncastrated but have been sent off in the winter due to the fence trashing above.
I am very very pro animal welfare but dont have any problems with the ringing, just cos I can see it isnt causing them a problem, I do it and then they are off investigating pen/straw/mum's sheep cob bucket straight away.
However I did go on a course to do lambing and learn how to ring properly AND I did do it under vet supervision the first few times. Maybe that should be compulsory. But I think the ringing should remain a matter of choice.
Tail ringing I think is less clear cut, since it would be possible to breed out long daggy tails, if that were prioritised. But while the tails are long, in certain areas of the country the right answer is to ring, but the real answer is to breed out long tails over time. I dont face this issue since Shetlands have naturally shorter tails and dont need to be docked.