Jonathan Shear casts much light on the issue of altering consciousness in pointing out that the validity of the skills or insights gained is really the ultimate issue, not whether the alterations are "abnormal" or not. If an inventor comes up with some of his or her best inventions while drunk, we're still glad they were invented, and hope the liver damage isn't too bad so they will stick around to continue inventing. Where Shear's perspective is a bit too narrow, however, is where he asks us to evaluate the products of the altered states
as measured in terms of the things we are ordinarily concerned with.
That's fine as far as it goes: if being a mystic makes you a better mathematician, great. But let's remember that the point of pursuing most consciousness altering disciplines is to have insight into things that are beyond or not readily measured by the things we are ordinarily concerned with. A mystical insight at a deep level that the universe is inherently intelligent, meaningful and in harmony, e.g., is deeply satisfying to the mystic but not really evaluatable by ordinary criteria.
Thus my proposal in Science back in the 70s to create state-specific sciences if we want to understand the whole spectrum of consciousness. Rather than just accept that some people have extra-ordinary insights that make no sense in ordinary consciousness so we can't evaluate them, we would like to know if they have an inherent sense of their own or are mere idiosyncratic ramblings or pathologies. Thus we train observers/scientists to enter the desired altered states, makes observations from within the states, theorize within the states, share their observations and theories with each other, refining this process over time, and thus seeing if trained observers can agree on what it's all about, even if we "outsiders" can't really understand what they do.
It's rather like physics. It takes a special induction procedure lasting anywhere from 8 to 10 years to reshape the persons's mind so they actually understand most of what modern physics is about.