This is the point I wanted to bring up but was too laze to write... :P
LHO's should be given freedom to decide what's a spoiler or not, for themselves, after all they have earned that responsibility. They would know what's fit to be told and what's not, at the moment when the question is being asked. If the LHO's are forced to say "Sorry, that's a spoiler. Try to figure out yourself and if you can't, I may give a hint" all the time, what's so hard about saying that? Anyone can do that, if they have solved the same thing before. So are LHO's no different from normal people as far as "teaching" goes?
And then again, there are many different ways people interpret "teaching". Some would say that you ask questions to make someone realize the answer, some would say that you give them direct answers, etc. What really matters is that people should realize why an LHO has acted to teach the way he/she has. If there's a reason he has not considered something a spoiler, I do think that no one has the right to say "no but that's still a spoiler since everyone says so and the old players also worked hard for it and not by spoilers and bla bla bla". After all, an LHO interacting with someone new would know how that person likes to learn.