Not because life is sacred, or because life is always worth living no matter the suffering, no; instead because (a we aren't utility-calculating robots and (b because few effective suicide methods are available that don't run the risk of you becoming brain-damaged due to 'rescue'. And while it is somewhat liberating to turn to someone and say, "I don't actually have to take your shit, I can just go kill myself whenever I want, so there, poo-poo to you sir/madam", the constant thoughts of escaping beyond fiction aren't good for you. In my experience, in fact, they hurt. A lot. But is it intellectual cowardice to act otherwise? When you are in a horrible situation, is it better to be honest with yourself? Say you are trapped in a padded prison cell (for whatever reason you think fits). Should you torture yourself more by thinking of escape (in case you might actually find a way), or should you instead pretend you aren't in that situation at all? I guess I've committed something of a fallacy there - maybe you can stop thinking about your situation. And I'm not particularly sure that it is in fact more honest to think about your death if you so crave it. So all in all, even if it seems like you are not facing up to what is currently your greatest desire, it does seem logical to cease thinking about suicide, simply because being aware that you are suffering and trapped etc. doesn't actually reduce your suffering. No, instead it actually INCREASES it. Which, at first glance, actually seems quite strange to me. I was stuck in the mindset for a while there that it was good to be suicidal, good to think about my death, because I was being true to myself. But I think if I were really being true to myself, I'd be scrounging for as much non-suffering as possible, so I'd be serving more in the long run my need for true-to-myself-ness, even if in the short term I'd be fooling myself a little.
So you, (or more to my rambling point, I) shouldn't think about suicide unless the means are available to do it, because along with the fact that suicidal thoughts are painful, they are also usually quite a bit emotionally biased - you don't see numerical data scrolling down when you think about it, for example. So sorry for re-affirming what everyone already knew anyway, this is simply something that is new to me, strangely.