If, as the average person believes, struggle and horror make life worth living, build character, and teach us lessons, then why isn't anyone deliberately creating horrible situations for him- or herself? The sheer size of the anti-smoking collective is enough to demonstrate that most people are not interested in imposing harmful or deleterious agents on themselves, so why do the most pretentious among us continue to lie when stating that they find the most awful aspects of life to be the reasons for why life is worth living? Such aspects do not build character or make the good more good.
If you think otherwise, then why aren't you trying to get lung cancer by starting smoking? Why aren't you trying to get AIDS by having unprotected sex? Why aren't you chopping your arms off? If you want the good to be so good, then why aren't you making the bad as bad as it can be for yourself? Don't you want to spend the rest of your life in a wheelchair in order to prove that you're a strong person whose life is rich and worthwhile? If not, then cognitive dissonance, that most vile and disgusting of all meme viruses, has taken root inside your brain.
Of course, some might claim that, in order to be truly valuable, the bad cannot be administered consciously. This is silly on its face, as the only difference between the above set of circumstances and this one is that, in this case, there is a lack of reason and deliberation. It could be said, then, that mystery is what those who subscribe to this view are after, and, unfortunately, humans do value mystery, often for idiotic evolutionary reasons: we eventually became intelligent animals, but did not fully understand our world, so we had no choice but to evolve reverence for the unknowable and mysterious.