Kalosyni let's pursue these issues as deeply and at length as you are inclined to do so. And it's good to write them in the public threads too, because they have come up many times before and will come up many times in the future. I can't easily find cites, but just as Don is engaged now, he's always been interested in these issues too -- you will find in past thread many exchanges with Don and Elayne as well on these topics.
A significant part of the question involves how hard it is to accept that strongly-held beliefs may not be grounded in a view of nature that is "provable" to be universal. All of us have deeply held views which we find highly pleasurable to support and abhorrent to find challenged, and that is as it should be because our sense of pleasure and pain does not all work the same way for everyone.
But what Epicurus did was say something like: "I don't care if the truth doesn't support my own view of pleasure and pain, I want to know the facts of nature and what is true, and I'll deal with the consequences." It is only because he came to firm conclusions about the nature of the universe that he concluded it to be impossible for there to be absolute justice or absolute rules of anything -- rules imply rule-givers and rule-enforcers, and those just don't exist - at least to our liking of them. Yes in the end the way humans work means that often times people we consider to be "bad" will be punished by other people as a result of their actions. But the bitter truth is that that is not always so, and often people we consider to be bad prosper and people we consider to be good get ground in the dust. And to make matters worse, Epicurus emphasizes that there is no compensation for such "unfairness" after death -- there IS no life after death where the good are rewarded and the bad are punished.
All of which means not that we shouldn't fight for what we find pleasing and fight against what we find painful, but only that we have to be realistic that there are no supernatural forces fighting on our side. Even more, it means that if WE don't take action to fight for our tranquility and to fight against the forces both mental and physical that would take that from us, then it's very possible (and maybe likely, if we're unlucky) that we and our friends are going to die an early and miserable death because of our failure to take proper action.
And when you add to that that Epicurus taught that there is "no fate" in human affairs, then you've got a philosophy that isn't left-wing or right-wing or center in political terms, but is highly charged with personal responsibility. Even if we work as hard as we can for our pleasure and tranquility no paradise is guaranteed to us, but the way the world operates if we DON't Work as hard as we can, then we're very likely to miss out on the good things in life that might well be ours if we lean and apply a true philosophy.