Many thanks to all of you who took the time to offer your insightful thoughts and comments on my previous post. I don't know if I can respond to all of your comments in a way that does justice to their insightfulness, but I'll try.
Fran, I like the distinction that you make between the 2 questions. In writing the post, I was probably being insensitive to the fact that torture commonly refers to the kind of unspeakable physical and mental suffering that, unfortunately, still occurs daily in this world, and which, unfortunately, is often perpetrated by people who claim to be fighting for freedom and good. My apologies for this insensitivity, although there is actually still a part of me that continues to wonder whether what we call physical discomfort/effort and what we commonly refer to as torture might not be different points on the same spectrum. (Perhaps there is only one way to find out: Get somebody to water-board me! But I'll pass on that...) So I'll have to leave my wondering at this.
But fortunately, I don't have to settle the "what exactly is torture" question in order to ask my question. I can easily rephrase my question in my previous post as: Why on earth are we subjecting ourselves on a daily basis to something that is so difficult and challenging, and which, for many of us, causes so much physical and mental discomfort, and possibly even pain? (Hmm... I think you can already see that this way of putting the question simply doesn't have the in-your-face provocative quality of my orginal question :-))
Cathrine, I like your answer to the question, which is that we do this in order to achieve greatness, however that might be construed among different practitioners.
Another possible answer, inspired by OvO's comments, is that the practice gives us a safe space in which to allow our self-loathing and other negativities (or the Dark Side, if you are a Star Wars geek) to surface, and to examine these negativities without necessarily acting upon them (in Star Wars parlance: To experience what it is like to be a Sith Lord without actually morphing into a Sith Lord). So in this sense (if I understand you correctly, OvO), the practice acts as a sort of mental/emotional elimination process: Just as physical waste that is not eliminated from our bodies will fester and make us sick, mental/emotional baggage that is not discharged from our lives will also "fester" and hinder us from becoming fully realized human beings.
But we also know that the mental/emotional elimination process is by no means easy and smooth sailing. Sometimes, it may be that the particular method of practice that we choose to engage in (ashtanga, zen meditation, bikram, or whatever your chosen method is) is working on us so intensely that we have to put the brakes on it, so to speak, and re-engage the process at a later time, when we feel more ready. Or we might have to re-evaluate, and decide whether this particular process/method is the right process/method for us. All of which brings up another question: How do we know when it is time to (1) keep working with the process, or (2) put on the brakes for a little bit, and come back to it later, or (3) change to a totally different method/process altogether?