Your original claim was that everyone wants happiness, and doesn't want unhappiness, without qualification, I only desired to show that this isn't quite true, that both there are things far more valuable than happiness, and that happiness isn't desirable if brought about by certain causes.
Your point now is also simplistic, and takes an unqualified position on pain. You know if you take a bunch of pain killers for long enough, then it will greatly reduce your pain tolerance thresholds. Without experiencing any pain, we will become less and less able to tolerate pain. What doesn't kill you makes you stronger, and all that. Taking an unqualified position on pain can also lead to unhealthy circumstances. Even "too much health" is bad, in the sense that the immune system grows and matures, and if completely sheltered from germs, dirt, or sickness, then it cannot develop, and you will become much more susceptible to sickness in later life.
You don't go into why they wish not to prevent it? A proper evaluation requires efforts, risks, involvements, and costs. Just that it is possible for them to prevent it doesn't cover what preventing it may entail. The trolley thought experiment could be worded just as "something bad going to happen" that you could prevent, but since what it is, how you'd prevent it, and all of the variables, the implied obviousness of not doing so being unreasonable is not justified. We live in a complex world is my very point, even if doing something takes five seconds, that's still a cost, and five seconds you could have been doing something else.
As for if I owed someone something, and they didn't feel like paying it, so was like, "nah son, I ain't paying" then they wouldn't like it, and there may be consequences like them not helping you, or speaking to you again, trying to attack you or some shit, but you can still do it.
As for yourself, if say, I spend extra money out of the budget, this pay check, obliging future me to contribute more to the bills out of the next one, I can say "nah fuck that". Or if you don't like that, then if I make a promise to myself to change a habit or some such, but then don't follow through, I'm not only going to feel bad about it, but I'm going to take myself less seriously the next time I proclaim such a obligation to myself, and develop a sense of myself as untrustworthy, and unreliable when speaking about such things.