As far as injecting steriods goes, I think in can be a terrific theraputic protocol if combined with an appropriate period of rest and a carreer change.
For instance, "A" rated medium pony with arthritic hocks has hocks injected and is given a year off and then brought back slowly as a local and lesson pony, jumping lower fences. No problem.
Same medium pony, same hocks, injected so he can continue showing every weekend and go to indoors? In other words, continue doing the same work that made him lame, at the same intensity, but use the steriods to cover up the lameness because of an owner's ambition? I've got lot of problems with that scenario.
I'm assuming we're talking about nerving being one or both of the nerves in the horse's heel; I don't think many vets would agree to do the middle of the hoof or the toe. Also, nerving is in no way theraputic, unlike steriod injections. All you're doing is stopping the pain message from getting to the brain.
Making a decision about nerving should be subject to similiar considerations as steriod injections - are you doing it for the animal or is it a means to a competitive end? Doing it to meet a competive end isn't necessarily bad, but it means you have to look that much closer at the long range aspects. I think the biggest consideraton about nerving is that you must be willing to closely supervise the horse's care for the rest of it's life - no just turning it out in the pasture.
If you nerve the horse to return it to soundness, return it to work at a lower intensity than before it developed heel pain and can guarantee the horse will recieve decent care in retirement, I don't have a problem with it.
If you're talking about nerving tails, that I have a huge problem with, because no one can possibly guarantee that the poor animanl will never be in as situation where in needs to switch a fly again as long as it lives.