Right, I think I understand all of your individual points, but I don't understand how it all adds up to us not being in agreement. So yes, there's still something that one of us isn't understanding about the other's argument.
And in that vein, I am wondering if perhaps I've been too loose with some of my language, particularly my usage of the words "happiness" and "pleasure". Ultimately, what I mean by either of those words, is simply "feeling good".
That said, I do recognize that "happiness" tends to refer to "emotional" or "mental" feelings, while "pleasure" tends to refer to "physical" feelings. And along those lines, I think there is some recognition that physical feelings tend to be relatively immutable and non-negotiable, compared to emotional feelings, which can depend a lot on the narrative you've spun around those feelings. For instance, slamming my finger in a door will always hurt, no matter who I am, whereas my feelings about Trump getting elected depends on a complex system of beliefs and social ties.
And in light of those connotations, I do tend to use the words "pleasure" and "pain" when trying to elucidate the irrefutably intrinsic value and fundamentally motivational power of good and bad feelings - and therefore to imply them as a fundamental value system of the universe. Whereas I tend to use the terms "happiness" and "sadness" as a shorthand way to refer to a more generic, holistic, or all encompassing state of "feeling good" or "feeling bad" as a sum total of all pleasure, pain, happiness, and sadness for a given person.
But having said all that, it's of course still not entirely accurate to think of physical feelings as inevitable and emotional feelings as negotiable. Because, for instance, the physical discomfort of a long plane ride, or a feeling ill, can be largely forgotten if your attention is drawn elsewhere, like by watching a good movie. And on the flipside, emotional pain may be quite persistent despite a personal narrative that would seek to dismiss or reinterpret it. A person might feel instinctively ashamed or proud of their parents' crimes or achievements, despite a belief that a parent's actions should not reflect on their children at all.
And along those lines, we've of course found many ways to manipulate our feelings, semi-independently of our circumstances. Drugs, entertainment, and hot showers are some of the ways. And other people do it via meditation, finding ways to dissociate, or redirect their attention, so that physical pain loses some of its bite, and emotional pain can be reimagined as something to grow from, and therefore, to feel better about. But either way, the goal is always the same: to discover ways to feel more good, and to feel less bad.
I haven't really addressed your bug analogy, so I'll do so now.
To start, I think it depends on how we think the bug feels about bumping the light. Let's assume, for the moment, that it feels great, and that the bug ultimately dies happy, albeit without reproducing.
And I think we could really just compare that to a couple that chooses not to have children. Many couples choose not to have children, because they think they will enjoy life more without them. This is very similar to the bug bumping the light. In a sense, it is a failure of evolution. Because they will obviously not pass on their genes. From an evolutionary perspective, this is the same decision as suicide.
But we, in western society anyway, generally accept this as a perfectly acceptable decision. And it's acceptable because it makes them happy (i.e. feel good), and doesn't force sadness (i.e. bad feelings) on anyone else.
Next, let's imagine that the bug doesn't like bumping the light, and that they experience a constant state of frustration.
I think we could compare that bug to a lot of people in the modern world - anyone who's bought into some idea of what's "good" or a "moral" or "right", that doesn't specifically have "feeling good" as it's goal. There are tons of people who, in the name of love, morality, or pride, bring a fair share of misery and frustration upon themselves and others. They keep blindly bumping towards their one ill-conceived goal, rather than chasing the one thing that is always its own reward - which is to say, "feeling good".
Once people stop chasing and bumping the "bug light" of love, morality, pride, wealth, or whatever else they've idolized, and instead start chasing happiness (i.e. good feelings), then they will be more likely to feel good, and less likely to get in the way of other people feeling good.
And what more could anyone want than that? How can any person's "wanting" ever have as its goal anything other than "feeling good", and not "feeling bad"?
That's ultimately my thesis. That any sufficiently introspective person will always be able to recognize that anything they ever want or fear can always be described in terms of how they prefer to feel. And the way they prefer to feel is "good" or "happy", and not "bad" or "sad" or "in pain".
And from the perspective of myself - or, I assume, that of any other individual person or sentient being - we can adopt no other value system or motivational framework that supersedes the intrinsic value of those good and bad feelings, and the desire to experience the former, and the fear of experiencing the latter.